From c5cbe335664f9218f7689d8c3baa56d3437e8674 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 06:35:56 +0000
Subject: [PATCH 01/12] Add gg() shorthand alias for g2(), inspired by
 tinyplot's plt()

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/df53ceb6-3fa6-43d1-aba3-b50da99ad847

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 DESCRIPTION                |  2 +-
 NAMESPACE                  |  1 +
 R/gglite.R                 | 10 ++++++++++
 man/gg.Rd                  | 40 ++++++++++++++++++++++++++++++++++++++
 tests/testit/test-gglite.R |  7 +++++++
 5 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 man/gg.Rd

diff --git a/DESCRIPTION b/DESCRIPTION
index a9990fc..05d3a06 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: gglite
 Title: Lightweight Data Visualization via the Grammar of Graphics
-Version: 0.0.10
+Version: 0.0.11
 Authors@R: person("Yihui", "Xie", role = c("aut", "cre"), email = "xie@yihui.name",
     comment = c(ORCID = "0000-0003-0645-5666"))
 Description: A lightweight R interface to the AntV G2 JavaScript visualization
diff --git a/NAMESPACE b/NAMESPACE
index a4c897f..305571a 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -20,6 +20,7 @@ export(facet_circle)
 export(facet_rect)
 export(g2)
 export(g2Output)
+export(gg)
 export(interact)
 export(labels_)
 export(legend_)
diff --git a/R/gglite.R b/R/gglite.R
index 81b96b8..e931e2a 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -128,4 +128,14 @@ encode = function(chart, ...) {
   chart
 }
 
+#' Shorthand Alias for [g2()]
+#'
+#' `gg()` is a convenient shorthand for [g2()], inspired by tinyplot's `plt()`
+#' alias. All arguments are passed through to [g2()].
+#'
+#' @inheritParams g2
+#' @export
+#' @examples
+#' gg(mtcars, x = 'mpg', y = 'hp')
+gg = g2
 
diff --git a/man/gg.Rd b/man/gg.Rd
new file mode 100644
index 0000000..3f60b5d
--- /dev/null
+++ b/man/gg.Rd
@@ -0,0 +1,40 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/gglite.R
+\name{gg}
+\alias{gg}
+\title{Shorthand Alias for \code{\link[=g2]{g2()}}}
+\usage{
+gg(
+  data = NULL,
+  ...,
+  width = 640,
+  height = 480,
+  padding = NULL,
+  margin = NULL,
+  inset = NULL
+)
+}
+\arguments{
+\item{data}{A data frame, a \code{ts}/\code{mts} time series object, or \code{NULL}. Time
+series objects are automatically converted to data frames (with columns
+\code{time} and \code{value} for univariate series, or \code{time}, \code{series}, and \code{value}
+for multivariate series) and default aesthetic mappings are set
+accordingly.}
+
+\item{...}{Aesthetic mappings as \code{name = 'column'} pairs (character strings),
+or a formula followed by optional named aesthetics.}
+
+\item{width, height}{Width and height of the chart in pixels.}
+
+\item{padding, margin, inset}{Layout spacing in pixels. Each can be a scalar
+(applied to all sides) or a length-4 vector \code{c(top, right, bottom, left)};
+use \code{NA} to skip individual sides. \code{NULL} (the default) leaves the value
+unset.}
+}
+\description{
+\code{gg()} is a convenient shorthand for \code{\link[=g2]{g2()}}, inspired by tinyplot's \code{plt()}
+alias. All arguments are passed through to \code{\link[=g2]{g2()}}.
+}
+\examples{
+gg(mtcars, x = 'mpg', y = 'hp')
+}
diff --git a/tests/testit/test-gglite.R b/tests/testit/test-gglite.R
index 68d5df2..732ebcb 100644
--- a/tests/testit/test-gglite.R
+++ b/tests/testit/test-gglite.R
@@ -103,3 +103,10 @@ assert('g2() formula ~ x1 + x2 + x3 sets position encoding', {
     c('Sepal.Length', 'Sepal.Width', 'Petal.Length'))
   (is.null(chart$aesthetics$x))
 })
+
+assert('gg() is a shorthand alias for g2()', {
+  chart = gg(mtcars, x = 'mpg', y = 'hp')
+  (inherits(chart, 'g2'))
+  (chart$aesthetics$x %==% 'mpg')
+  (chart$aesthetics$y %==% 'hp')
+})

From 836b299f82817ee532e108b390ce830cf6eecfd1 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 06:37:47 +0000
Subject: [PATCH 02/12] Add main/sub title arguments to g2(), inspired by
 tinyplot and base plot()

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/df53ceb6-3fa6-43d1-aba3-b50da99ad847

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 R/gglite.R                 | 13 +++++++++++--
 man/g2.Rd                  | 12 +++++++++++-
 man/gg.Rd                  |  9 ++++++++-
 tests/testit/test-gglite.R | 11 +++++++++++
 4 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/R/gglite.R b/R/gglite.R
index e931e2a..5645586 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -52,6 +52,9 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'   (applied to all sides) or a length-4 vector `c(top, right, bottom, left)`;
 #'   use `NA` to skip individual sides. `NULL` (the default) leaves the value
 #'   unset.
+#' @param main Chart title string, a convenient alternative to calling
+#'   [title_()] separately (inspired by base [plot()] and tinyplot).
+#' @param sub Chart subtitle string. Only used when `main` is also provided.
 #' @return A `g2` object (S3 class).
 #' @import stats utils
 #' @export
@@ -66,9 +69,13 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #' # Time series
 #' g2(sunspot.year)
 #' g2(EuStockMarkets)
+#'
+#' # Title and subtitle (like base plot's main/sub)
+#' g2(mtcars, hp ~ mpg, main = 'Motor Trend Cars', sub = 'mpg vs hp')
 g2 = function(
   data = NULL, ..., width = 640, height = 480,
-  padding = NULL, margin = NULL, inset = NULL
+  padding = NULL, margin = NULL, inset = NULL,
+  main = NULL, sub = NULL
 ) {
   dots = list(...)
   has_formula = length(dots) && inherits(dots[[1]], 'formula')
@@ -99,7 +106,9 @@ g2 = function(
     theme = NULL,
     axes = list(),
     legends = list(),
-    chart_title = NULL,
+    chart_title = if (!is.null(main)) {
+      if (!is.null(sub)) list(title = main, subtitle = sub) else main
+    },
     facet = facet_from_formula,
     layout = c(
       process_layout('padding', padding),
diff --git a/man/g2.Rd b/man/g2.Rd
index 01ceb78..44afdb9 100644
--- a/man/g2.Rd
+++ b/man/g2.Rd
@@ -11,7 +11,9 @@ g2(
   height = 480,
   padding = NULL,
   margin = NULL,
-  inset = NULL
+  inset = NULL,
+  main = NULL,
+  sub = NULL
 )
 }
 \arguments{
@@ -30,6 +32,11 @@ or a formula followed by optional named aesthetics.}
 (applied to all sides) or a length-4 vector \code{c(top, right, bottom, left)};
 use \code{NA} to skip individual sides. \code{NULL} (the default) leaves the value
 unset.}
+
+\item{main}{Chart title string, a convenient alternative to calling
+\code{\link[=title_]{title_()}} separately (inspired by base \code{\link[=plot]{plot()}} and tinyplot).}
+
+\item{sub}{Chart subtitle string. Only used when \code{main} is also provided.}
 }
 \value{
 A \code{g2} object (S3 class).
@@ -66,4 +73,7 @@ g2(mtcars, ~ mpg)
 # Time series
 g2(sunspot.year)
 g2(EuStockMarkets)
+
+# Title and subtitle (like base plot's main/sub)
+g2(mtcars, hp ~ mpg, main = 'Motor Trend Cars', sub = 'mpg vs hp')
 }
diff --git a/man/gg.Rd b/man/gg.Rd
index 3f60b5d..c2b4fb7 100644
--- a/man/gg.Rd
+++ b/man/gg.Rd
@@ -11,7 +11,9 @@ gg(
   height = 480,
   padding = NULL,
   margin = NULL,
-  inset = NULL
+  inset = NULL,
+  main = NULL,
+  sub = NULL
 )
 }
 \arguments{
@@ -30,6 +32,11 @@ or a formula followed by optional named aesthetics.}
 (applied to all sides) or a length-4 vector \code{c(top, right, bottom, left)};
 use \code{NA} to skip individual sides. \code{NULL} (the default) leaves the value
 unset.}
+
+\item{main}{Chart title string, a convenient alternative to calling
+\code{\link[=title_]{title_()}} separately (inspired by base \code{\link[=plot]{plot()}} and tinyplot).}
+
+\item{sub}{Chart subtitle string. Only used when \code{main} is also provided.}
 }
 \description{
 \code{gg()} is a convenient shorthand for \code{\link[=g2]{g2()}}, inspired by tinyplot's \code{plt()}
diff --git a/tests/testit/test-gglite.R b/tests/testit/test-gglite.R
index 732ebcb..7aa7fed 100644
--- a/tests/testit/test-gglite.R
+++ b/tests/testit/test-gglite.R
@@ -110,3 +110,14 @@ assert('gg() is a shorthand alias for g2()', {
   (chart$aesthetics$x %==% 'mpg')
   (chart$aesthetics$y %==% 'hp')
 })
+
+assert('g2() main argument sets chart title', {
+  chart = g2(mtcars, x = 'mpg', y = 'hp', main = 'My Title')
+  (chart$chart_title %==% 'My Title')
+})
+
+assert('g2() main and sub arguments set title and subtitle', {
+  chart = g2(mtcars, x = 'mpg', y = 'hp', main = 'Title', sub = 'Subtitle')
+  (chart$chart_title$title %==% 'Title')
+  (chart$chart_title$subtitle %==% 'Subtitle')
+})

From 75d5d4b32511cb594da18dfedfb6e5c0dc2b136f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 06:39:05 +0000
Subject: [PATCH 03/12] Add by argument for color grouping in g2(), inspired by
 tinyplot's by

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/df53ceb6-3fa6-43d1-aba3-b50da99ad847

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 R/gglite.R                 |  9 ++++++++-
 man/g2.Rd                  | 10 +++++++++-
 man/gg.Rd                  |  7 ++++++-
 tests/testit/test-gglite.R |  5 +++++
 4 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/R/gglite.R b/R/gglite.R
index 5645586..b9c3ee5 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -55,6 +55,9 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #' @param main Chart title string, a convenient alternative to calling
 #'   [title_()] separately (inspired by base [plot()] and tinyplot).
 #' @param sub Chart subtitle string. Only used when `main` is also provided.
+#' @param by Column name (character string) to group the data by color,
+#'   inspired by tinyplot's `by` argument. Equivalent to passing
+#'   `color = 'column'`.
 #' @return A `g2` object (S3 class).
 #' @import stats utils
 #' @export
@@ -72,10 +75,13 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'
 #' # Title and subtitle (like base plot's main/sub)
 #' g2(mtcars, hp ~ mpg, main = 'Motor Trend Cars', sub = 'mpg vs hp')
+#'
+#' # Grouping by color (like tinyplot's by argument)
+#' g2(iris, Sepal.Length ~ Sepal.Width, by = 'Species')
 g2 = function(
   data = NULL, ..., width = 640, height = 480,
   padding = NULL, margin = NULL, inset = NULL,
-  main = NULL, sub = NULL
+  main = NULL, sub = NULL, by = NULL
 ) {
   dots = list(...)
   has_formula = length(dots) && inherits(dots[[1]], 'formula')
@@ -117,6 +123,7 @@ g2 = function(
     )
   ), class = 'g2')
   if (length(dots)) chart$aesthetics = modifyList(chart$aesthetics, dots)
+  if (!is.null(by)) chart$aesthetics$color = by
   chart
 }
 
diff --git a/man/g2.Rd b/man/g2.Rd
index 44afdb9..e8d1a68 100644
--- a/man/g2.Rd
+++ b/man/g2.Rd
@@ -13,7 +13,8 @@ g2(
   margin = NULL,
   inset = NULL,
   main = NULL,
-  sub = NULL
+  sub = NULL,
+  by = NULL
 )
 }
 \arguments{
@@ -37,6 +38,10 @@ unset.}
 \code{\link[=title_]{title_()}} separately (inspired by base \code{\link[=plot]{plot()}} and tinyplot).}
 
 \item{sub}{Chart subtitle string. Only used when \code{main} is also provided.}
+
+\item{by}{Column name (character string) to group the data by color,
+inspired by tinyplot's \code{by} argument. Equivalent to passing
+\code{color = 'column'}.}
 }
 \value{
 A \code{g2} object (S3 class).
@@ -76,4 +81,7 @@ g2(EuStockMarkets)
 
 # Title and subtitle (like base plot's main/sub)
 g2(mtcars, hp ~ mpg, main = 'Motor Trend Cars', sub = 'mpg vs hp')
+
+# Grouping by color (like tinyplot's by argument)
+g2(iris, Sepal.Length ~ Sepal.Width, by = 'Species')
 }
diff --git a/man/gg.Rd b/man/gg.Rd
index c2b4fb7..50e0d1a 100644
--- a/man/gg.Rd
+++ b/man/gg.Rd
@@ -13,7 +13,8 @@ gg(
   margin = NULL,
   inset = NULL,
   main = NULL,
-  sub = NULL
+  sub = NULL,
+  by = NULL
 )
 }
 \arguments{
@@ -37,6 +38,10 @@ unset.}
 \code{\link[=title_]{title_()}} separately (inspired by base \code{\link[=plot]{plot()}} and tinyplot).}
 
 \item{sub}{Chart subtitle string. Only used when \code{main} is also provided.}
+
+\item{by}{Column name (character string) to group the data by color,
+inspired by tinyplot's \code{by} argument. Equivalent to passing
+\code{color = 'column'}.}
 }
 \description{
 \code{gg()} is a convenient shorthand for \code{\link[=g2]{g2()}}, inspired by tinyplot's \code{plt()}
diff --git a/tests/testit/test-gglite.R b/tests/testit/test-gglite.R
index 7aa7fed..33b4826 100644
--- a/tests/testit/test-gglite.R
+++ b/tests/testit/test-gglite.R
@@ -121,3 +121,8 @@ assert('g2() main and sub arguments set title and subtitle', {
   (chart$chart_title$title %==% 'Title')
   (chart$chart_title$subtitle %==% 'Subtitle')
 })
+
+assert('g2() by argument sets color aesthetic', {
+  chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', by = 'Species')
+  (chart$aesthetics$color %==% 'Species')
+})

From 43b1356b54dd5b6a0b3b344749d19dbacffa5ff5 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 06:42:28 +0000
Subject: [PATCH 04/12] Change formula | to color grouping, add facet param to
 g2() (tinyplot convention)

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/df53ceb6-3fa6-43d1-aba3-b50da99ad847

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 R/gglite.R                 | 37 +++++++++++++++++++++++++++++++------
 R/utils.R                  | 17 ++++-------------
 man/g2.Rd                  | 19 ++++++++++++++++---
 man/gg.Rd                  |  8 +++++++-
 tests/testit/test-gglite.R | 24 ++++++++++++++++++------
 tests/testit/test-utils.R  | 12 +++++-------
 vignettes/gglite.Rmd       |  8 +++++++-
 7 files changed, 88 insertions(+), 37 deletions(-)

diff --git a/R/gglite.R b/R/gglite.R
index b9c3ee5..d7ea243 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -34,8 +34,8 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'   \item{`~ x`}{Maps only `x` (e.g., for histograms or bar counts).}
 #'   \item{`~ x1 + x2 + x3`}{Creates a `position` encoding with multiple
 #'     fields (for parallel coordinates).}
-#'   \item{`y ~ x | z`}{Facets the chart by `z` (column direction).}
-#'   \item{`y ~ x | z1 + z2`}{Facets by `z1` (columns) and `z2` (rows).}
+#'   \item{`y ~ x | z`}{Groups by `z` (maps to color), inspired by
+#'     tinyplot's formula convention.}
 #' }
 #' Additional aesthetics (e.g., `color`, `size`) can still be passed as named
 #' arguments alongside the formula.
@@ -58,6 +58,10 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #' @param by Column name (character string) to group the data by color,
 #'   inspired by tinyplot's `by` argument. Equivalent to passing
 #'   `color = 'column'`.
+#' @param facet Faceting specification: a one-sided formula (`~ z` for
+#'   column faceting, `y ~ x` for grid faceting), or a character string
+#'   naming the faceting variable. Inspired by tinyplot's `facet` argument.
+#'   For more control, use [facet_rect()] or [facet_circle()] instead.
 #' @return A `g2` object (S3 class).
 #' @import stats utils
 #' @export
@@ -78,17 +82,36 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'
 #' # Grouping by color (like tinyplot's by argument)
 #' g2(iris, Sepal.Length ~ Sepal.Width, by = 'Species')
+#'
+#' # Formula | for color grouping (tinyplot convention)
+#' g2(iris, Sepal.Length ~ Sepal.Width | Species)
+#'
+#' # Faceting via the facet argument (like tinyplot)
+#' g2(iris, Sepal.Length ~ Sepal.Width, facet = ~Species)
+#' g2(mtcars, hp ~ mpg, facet = gear ~ cyl)
 g2 = function(
   data = NULL, ..., width = 640, height = 480,
   padding = NULL, margin = NULL, inset = NULL,
-  main = NULL, sub = NULL, by = NULL
+  main = NULL, sub = NULL, by = NULL, facet = NULL
 ) {
   dots = list(...)
+  by_from_formula = NULL
   has_formula = length(dots) && inherits(dots[[1]], 'formula')
-  facet_from_formula = if (has_formula) {
+  if (has_formula) {
     parsed = parse_formula(dots[[1]])
     dots = c(parsed$aesthetics, dots[-1])
-    parsed$facet
+    by_from_formula = parsed$by
+  }
+  # Build facet from the facet argument (formula or character)
+  facet_config = if (inherits(facet, 'formula')) {
+    fterms = if (length(facet) == 3) {
+      list(y = deparse(facet[[2]]), x = deparse(facet[[3]]))
+    } else {
+      list(x = deparse(facet[[2]]))
+    }
+    list(type = 'facetRect', encode = fterms)
+  } else if (is.character(facet)) {
+    list(type = 'facetRect', encode = list(x = facet))
   }
   # Convert time series to data frame with default aesthetics
   ts_aes = NULL
@@ -115,7 +138,7 @@ g2 = function(
     chart_title = if (!is.null(main)) {
       if (!is.null(sub)) list(title = main, subtitle = sub) else main
     },
-    facet = facet_from_formula,
+    facet = facet_config,
     layout = c(
       process_layout('padding', padding),
       process_layout('margin', margin),
@@ -123,6 +146,8 @@ g2 = function(
     )
   ), class = 'g2')
   if (length(dots)) chart$aesthetics = modifyList(chart$aesthetics, dots)
+  # by argument (explicit or from formula |) sets color grouping
+  if (is.null(by) && !is.null(by_from_formula)) by = by_from_formula
   if (!is.null(by)) chart$aesthetics$color = by
   chart
 }
diff --git a/R/utils.R b/R/utils.R
index 14289f8..bce5778 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -129,10 +129,10 @@ parse_formula = function(f) {
   lhs = if (length(f) == 3) f[[2]]
   rhs = if (length(f) == 3) f[[3]] else f[[2]]
 
-  # Extract conditioning (facet) variables from |
-  facet_terms = NULL
+  # Extract conditioning (by/color) variable from |
+  by_term = NULL
   if (is.call(rhs) && identical(rhs[[1]], as.name('|'))) {
-    facet_terms = extract_terms(rhs[[3]])
+    by_term = deparse(rhs[[3]])
     rhs = rhs[[2]]
   }
 
@@ -147,14 +147,5 @@ parse_formula = function(f) {
     aesthetics$position = rhs_terms
   }
 
-  # Build facet
-  facet = NULL
-  if (length(facet_terms)) {
-    enc = list()
-    if (length(facet_terms) >= 1) enc$x = facet_terms[1]
-    if (length(facet_terms) >= 2) enc$y = facet_terms[2]
-    facet = list(type = 'facetRect', encode = enc)
-  }
-
-  list(aesthetics = aesthetics, facet = facet)
+  list(aesthetics = aesthetics, by = by_term)
 }
diff --git a/man/g2.Rd b/man/g2.Rd
index e8d1a68..4ad8b5c 100644
--- a/man/g2.Rd
+++ b/man/g2.Rd
@@ -14,7 +14,8 @@ g2(
   inset = NULL,
   main = NULL,
   sub = NULL,
-  by = NULL
+  by = NULL,
+  facet = NULL
 )
 }
 \arguments{
@@ -42,6 +43,11 @@ unset.}
 \item{by}{Column name (character string) to group the data by color,
 inspired by tinyplot's \code{by} argument. Equivalent to passing
 \code{color = 'column'}.}
+
+\item{facet}{Faceting specification: a one-sided formula (\code{~ z} for
+column faceting, \code{y ~ x} for grid faceting), or a character string
+naming the faceting variable. Inspired by tinyplot's \code{facet} argument.
+For more control, use \code{\link[=facet_rect]{facet_rect()}} or \code{\link[=facet_circle]{facet_circle()}} instead.}
 }
 \value{
 A \code{g2} object (S3 class).
@@ -60,8 +66,8 @@ argument after \code{data}:
 \item{\code{~ x}}{Maps only \code{x} (e.g., for histograms or bar counts).}
 \item{\code{~ x1 + x2 + x3}}{Creates a \code{position} encoding with multiple
 fields (for parallel coordinates).}
-\item{\code{y ~ x | z}}{Facets the chart by \code{z} (column direction).}
-\item{\code{y ~ x | z1 + z2}}{Facets by \code{z1} (columns) and \code{z2} (rows).}
+\item{\code{y ~ x | z}}{Groups by \code{z} (maps to color), inspired by
+tinyplot's formula convention.}
 }
 Additional aesthetics (e.g., \code{color}, \code{size}) can still be passed as named
 arguments alongside the formula.
@@ -84,4 +90,11 @@ g2(mtcars, hp ~ mpg, main = 'Motor Trend Cars', sub = 'mpg vs hp')
 
 # Grouping by color (like tinyplot's by argument)
 g2(iris, Sepal.Length ~ Sepal.Width, by = 'Species')
+
+# Formula | for color grouping (tinyplot convention)
+g2(iris, Sepal.Length ~ Sepal.Width | Species)
+
+# Faceting via the facet argument (like tinyplot)
+g2(iris, Sepal.Length ~ Sepal.Width, facet = ~Species)
+g2(mtcars, hp ~ mpg, facet = gear ~ cyl)
 }
diff --git a/man/gg.Rd b/man/gg.Rd
index 50e0d1a..6f993b0 100644
--- a/man/gg.Rd
+++ b/man/gg.Rd
@@ -14,7 +14,8 @@ gg(
   inset = NULL,
   main = NULL,
   sub = NULL,
-  by = NULL
+  by = NULL,
+  facet = NULL
 )
 }
 \arguments{
@@ -42,6 +43,11 @@ unset.}
 \item{by}{Column name (character string) to group the data by color,
 inspired by tinyplot's \code{by} argument. Equivalent to passing
 \code{color = 'column'}.}
+
+\item{facet}{Faceting specification: a one-sided formula (\code{~ z} for
+column faceting, \code{y ~ x} for grid faceting), or a character string
+naming the faceting variable. Inspired by tinyplot's \code{facet} argument.
+For more control, use \code{\link[=facet_rect]{facet_rect()}} or \code{\link[=facet_circle]{facet_circle()}} instead.}
 }
 \description{
 \code{gg()} is a convenient shorthand for \code{\link[=g2]{g2()}}, inspired by tinyplot's \code{plt()}
diff --git a/tests/testit/test-gglite.R b/tests/testit/test-gglite.R
index 33b4826..a4c70d8 100644
--- a/tests/testit/test-gglite.R
+++ b/tests/testit/test-gglite.R
@@ -82,19 +82,31 @@ assert('g2() formula with extra aesthetics', {
   (chart$aesthetics$color %==% 'Species')
 })
 
-assert('g2() formula with faceting y ~ x | z', {
+assert('g2() formula with | sets color grouping (tinyplot convention)', {
   chart = g2(iris, Sepal.Length ~ Sepal.Width | Species)
   (chart$aesthetics$x %==% 'Sepal.Width')
   (chart$aesthetics$y %==% 'Sepal.Length')
+  (chart$aesthetics$color %==% 'Species')
+  (is.null(chart$facet))
+})
+
+assert('g2() facet argument with one-sided formula', {
+  chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', facet = ~Species)
   (chart$facet$type %==% 'facetRect')
   (chart$facet$encode$x %==% 'Species')
 })
 
-assert('g2() formula with two facet variables', {
-  df = data.frame(x = 1, y = 2, a = 'A', b = 'B')
-  chart = g2(df, y ~ x | a + b)
-  (chart$facet$encode$x %==% 'a')
-  (chart$facet$encode$y %==% 'b')
+assert('g2() facet argument with two-sided formula', {
+  chart = g2(mtcars, x = 'mpg', y = 'hp', facet = gear ~ cyl)
+  (chart$facet$type %==% 'facetRect')
+  (chart$facet$encode$x %==% 'cyl')
+  (chart$facet$encode$y %==% 'gear')
+})
+
+assert('g2() facet argument with character string', {
+  chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', facet = 'Species')
+  (chart$facet$type %==% 'facetRect')
+  (chart$facet$encode$x %==% 'Species')
 })
 
 assert('g2() formula ~ x1 + x2 + x3 sets position encoding', {
diff --git a/tests/testit/test-utils.R b/tests/testit/test-utils.R
index 55428e1..da0f4b4 100644
--- a/tests/testit/test-utils.R
+++ b/tests/testit/test-utils.R
@@ -54,18 +54,16 @@ assert('parse_formula: ~ x1 + x2 + x3', {
   (is.null(res$aesthetics$x))
 })
 
-assert('parse_formula: y ~ x | z', {
+assert('parse_formula: y ~ x | z sets color grouping (not facet)', {
   res = parse_formula(hp ~ mpg | cyl)
   (res$aesthetics$x %==% 'mpg')
   (res$aesthetics$y %==% 'hp')
-  (res$facet$type %==% 'facetRect')
-  (res$facet$encode$x %==% 'cyl')
+  (res$by %==% 'cyl')
 })
 
-assert('parse_formula: y ~ x | z1 + z2', {
-  res = parse_formula(y ~ x | a + b)
-  (res$facet$encode$x %==% 'a')
-  (res$facet$encode$y %==% 'b')
+assert('parse_formula: no | returns NULL by', {
+  res = parse_formula(y ~ x)
+  (is.null(res$by))
 })
 
 assert('ts_to_df converts univariate ts', {
diff --git a/vignettes/gglite.Rmd b/vignettes/gglite.Rmd
index 8011024..0197bfe 100644
--- a/vignettes/gglite.Rmd
+++ b/vignettes/gglite.Rmd
@@ -67,12 +67,18 @@ Additional aesthetics like `color` can be passed alongside the formula:
 g2(iris, Sepal.Length ~ Sepal.Width, color = 'Species')
 ```
 
-Use `|` for faceting:
+Use `|` for color grouping (inspired by tinyplot):
 
 ```{r}
 g2(iris, Sepal.Length ~ Sepal.Width | Species)
 ```
 
+Use the `facet` argument for faceting (also inspired by tinyplot):
+
+```{r}
+g2(iris, Sepal.Length ~ Sepal.Width, facet = ~Species)
+```
+
 A one-sided formula maps only `x` (useful for histograms or counts):
 
 ```{r}

From 5f944a5259be3b73bdbddb7b7d2dd61ae4d15244 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 06:44:47 +0000
Subject: [PATCH 05/12] Add alpha convenience parameter for opacity, inspired
 by tinyplot

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/df53ceb6-3fa6-43d1-aba3-b50da99ad847

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 R/gglite.R                 | 10 +++++++++-
 R/render.R                 | 11 +++++++++++
 man/g2.Rd                  | 11 ++++++++++-
 man/gg.Rd                  |  8 +++++++-
 tests/testit/test-render.R | 15 +++++++++++++++
 5 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/R/gglite.R b/R/gglite.R
index d7ea243..dcd4b53 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -62,6 +62,10 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'   column faceting, `y ~ x` for grid faceting), or a character string
 #'   naming the faceting variable. Inspired by tinyplot's `facet` argument.
 #'   For more control, use [facet_rect()] or [facet_circle()] instead.
+#' @param alpha Numeric in `[0, 1]` controlling the fill and stroke opacity
+#'   of marks. A convenient alternative to calling
+#'   `style_mark(fillOpacity = ..., strokeOpacity = ...)`. Inspired by
+#'   tinyplot's `alpha` argument.
 #' @return A `g2` object (S3 class).
 #' @import stats utils
 #' @export
@@ -89,10 +93,13 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #' # Faceting via the facet argument (like tinyplot)
 #' g2(iris, Sepal.Length ~ Sepal.Width, facet = ~Species)
 #' g2(mtcars, hp ~ mpg, facet = gear ~ cyl)
+#'
+#' # Adjust opacity (like tinyplot's alpha)
+#' g2(iris, Sepal.Length ~ Sepal.Width | Species, alpha = 0.5)
 g2 = function(
   data = NULL, ..., width = 640, height = 480,
   padding = NULL, margin = NULL, inset = NULL,
-  main = NULL, sub = NULL, by = NULL, facet = NULL
+  main = NULL, sub = NULL, by = NULL, facet = NULL, alpha = NULL
 ) {
   dots = list(...)
   by_from_formula = NULL
@@ -139,6 +146,7 @@ g2 = function(
       if (!is.null(sub)) list(title = main, subtitle = sub) else main
     },
     facet = facet_config,
+    alpha = alpha,
     layout = c(
       process_layout('padding', padding),
       process_layout('margin', margin),
diff --git a/R/render.R b/R/render.R
index 87aad54..91c5dc5 100644
--- a/R/render.R
+++ b/R/render.R
@@ -97,6 +97,17 @@ build_config = function(chart) {
 
   if (length(marks)) config$children = marks
 
+  # Apply chart-level alpha to all marks
+  if (!is.null(chart$alpha)) {
+    a = chart$alpha
+    for (i in seq_along(config$children)) {
+      s = config$children[[i]]$style
+      if (is.null(s$fillOpacity)) s$fillOpacity = a
+      if (is.null(s$strokeOpacity)) s$strokeOpacity = a
+      config$children[[i]]$style = s
+    }
+  }
+
   # Chart-wide config
   if (length(chart$scales)) config$scale = chart$scales
   if (!is.null(chart$coords)) config$coordinate = chart$coords
diff --git a/man/g2.Rd b/man/g2.Rd
index 4ad8b5c..2255902 100644
--- a/man/g2.Rd
+++ b/man/g2.Rd
@@ -15,7 +15,8 @@ g2(
   main = NULL,
   sub = NULL,
   by = NULL,
-  facet = NULL
+  facet = NULL,
+  alpha = NULL
 )
 }
 \arguments{
@@ -48,6 +49,11 @@ inspired by tinyplot's \code{by} argument. Equivalent to passing
 column faceting, \code{y ~ x} for grid faceting), or a character string
 naming the faceting variable. Inspired by tinyplot's \code{facet} argument.
 For more control, use \code{\link[=facet_rect]{facet_rect()}} or \code{\link[=facet_circle]{facet_circle()}} instead.}
+
+\item{alpha}{Numeric in \verb{[0, 1]} controlling the fill and stroke opacity
+of marks. A convenient alternative to calling
+\code{style_mark(fillOpacity = ..., strokeOpacity = ...)}. Inspired by
+tinyplot's \code{alpha} argument.}
 }
 \value{
 A \code{g2} object (S3 class).
@@ -97,4 +103,7 @@ g2(iris, Sepal.Length ~ Sepal.Width | Species)
 # Faceting via the facet argument (like tinyplot)
 g2(iris, Sepal.Length ~ Sepal.Width, facet = ~Species)
 g2(mtcars, hp ~ mpg, facet = gear ~ cyl)
+
+# Adjust opacity (like tinyplot's alpha)
+g2(iris, Sepal.Length ~ Sepal.Width | Species, alpha = 0.5)
 }
diff --git a/man/gg.Rd b/man/gg.Rd
index 6f993b0..6d00c0c 100644
--- a/man/gg.Rd
+++ b/man/gg.Rd
@@ -15,7 +15,8 @@ gg(
   main = NULL,
   sub = NULL,
   by = NULL,
-  facet = NULL
+  facet = NULL,
+  alpha = NULL
 )
 }
 \arguments{
@@ -48,6 +49,11 @@ inspired by tinyplot's \code{by} argument. Equivalent to passing
 column faceting, \code{y ~ x} for grid faceting), or a character string
 naming the faceting variable. Inspired by tinyplot's \code{facet} argument.
 For more control, use \code{\link[=facet_rect]{facet_rect()}} or \code{\link[=facet_circle]{facet_circle()}} instead.}
+
+\item{alpha}{Numeric in \verb{[0, 1]} controlling the fill and stroke opacity
+of marks. A convenient alternative to calling
+\code{style_mark(fillOpacity = ..., strokeOpacity = ...)}. Inspired by
+tinyplot's \code{alpha} argument.}
 }
 \description{
 \code{gg()} is a convenient shorthand for \code{\link[=g2]{g2()}}, inspired by tinyplot's \code{plt()}
diff --git a/tests/testit/test-render.R b/tests/testit/test-render.R
index d437869..e1c44b1 100644
--- a/tests/testit/test-render.R
+++ b/tests/testit/test-render.R
@@ -215,3 +215,18 @@ assert('build_config ts y-axis title does not override user title', {
   config = build_config(chart)
   (config$axis$y$title %==% 'My Title')
 })
+
+assert('build_config applies alpha to mark styles', {
+  chart = g2(mtcars, x = 'mpg', y = 'hp', alpha = 0.3) |> mark_point()
+  config = build_config(chart)
+  (config$children[[1]]$style$fillOpacity %==% 0.3)
+  (config$children[[1]]$style$strokeOpacity %==% 0.3)
+})
+
+assert('build_config alpha does not override explicit mark style opacity', {
+  chart = g2(mtcars, x = 'mpg', y = 'hp', alpha = 0.3) |>
+    mark_point() |> style_mark(fillOpacity = 0.8)
+  config = build_config(chart)
+  (config$children[[1]]$style$fillOpacity %==% 0.8)
+  (config$children[[1]]$style$strokeOpacity %==% 0.3)
+})

From f5f066a09cb1623c9238b4403b2ea84dfe42617e Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 06:46:13 +0000
Subject: [PATCH 06/12] Add palette convenience parameter for color palettes,
 inspired by tinyplot

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/df53ceb6-3fa6-43d1-aba3-b50da99ad847

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 R/gglite.R                 | 11 ++++++++++-
 man/g2.Rd                  | 11 ++++++++++-
 man/gg.Rd                  |  8 +++++++-
 tests/testit/test-gglite.R |  5 +++++
 4 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/R/gglite.R b/R/gglite.R
index dcd4b53..4b5e4d6 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -66,6 +66,10 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'   of marks. A convenient alternative to calling
 #'   `style_mark(fillOpacity = ..., strokeOpacity = ...)`. Inspired by
 #'   tinyplot's `alpha` argument.
+#' @param palette Character string naming a color palette (e.g.,
+#'   `'category10'`, `'tableau10'`, `'set2'`). A convenient alternative to
+#'   calling `scale_color(palette = ...)`. Inspired by tinyplot's `palette`
+#'   argument.
 #' @return A `g2` object (S3 class).
 #' @import stats utils
 #' @export
@@ -96,10 +100,14 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'
 #' # Adjust opacity (like tinyplot's alpha)
 #' g2(iris, Sepal.Length ~ Sepal.Width | Species, alpha = 0.5)
+#'
+#' # Set color palette (like tinyplot's palette)
+#' g2(iris, Sepal.Length ~ Sepal.Width | Species, palette = 'set2')
 g2 = function(
   data = NULL, ..., width = 640, height = 480,
   padding = NULL, margin = NULL, inset = NULL,
-  main = NULL, sub = NULL, by = NULL, facet = NULL, alpha = NULL
+  main = NULL, sub = NULL, by = NULL, facet = NULL, alpha = NULL,
+  palette = NULL
 ) {
   dots = list(...)
   by_from_formula = NULL
@@ -157,6 +165,7 @@ g2 = function(
   # by argument (explicit or from formula |) sets color grouping
   if (is.null(by) && !is.null(by_from_formula)) by = by_from_formula
   if (!is.null(by)) chart$aesthetics$color = by
+  if (!is.null(palette)) chart$scales$color = list(palette = palette)
   chart
 }
 
diff --git a/man/g2.Rd b/man/g2.Rd
index 2255902..37aa04c 100644
--- a/man/g2.Rd
+++ b/man/g2.Rd
@@ -16,7 +16,8 @@ g2(
   sub = NULL,
   by = NULL,
   facet = NULL,
-  alpha = NULL
+  alpha = NULL,
+  palette = NULL
 )
 }
 \arguments{
@@ -54,6 +55,11 @@ For more control, use \code{\link[=facet_rect]{facet_rect()}} or \code{\link[=fa
 of marks. A convenient alternative to calling
 \code{style_mark(fillOpacity = ..., strokeOpacity = ...)}. Inspired by
 tinyplot's \code{alpha} argument.}
+
+\item{palette}{Character string naming a color palette (e.g.,
+\code{'category10'}, \code{'tableau10'}, \code{'set2'}). A convenient alternative to
+calling \code{scale_color(palette = ...)}. Inspired by tinyplot's \code{palette}
+argument.}
 }
 \value{
 A \code{g2} object (S3 class).
@@ -106,4 +112,7 @@ g2(mtcars, hp ~ mpg, facet = gear ~ cyl)
 
 # Adjust opacity (like tinyplot's alpha)
 g2(iris, Sepal.Length ~ Sepal.Width | Species, alpha = 0.5)
+
+# Set color palette (like tinyplot's palette)
+g2(iris, Sepal.Length ~ Sepal.Width | Species, palette = 'set2')
 }
diff --git a/man/gg.Rd b/man/gg.Rd
index 6d00c0c..728b3a9 100644
--- a/man/gg.Rd
+++ b/man/gg.Rd
@@ -16,7 +16,8 @@ gg(
   sub = NULL,
   by = NULL,
   facet = NULL,
-  alpha = NULL
+  alpha = NULL,
+  palette = NULL
 )
 }
 \arguments{
@@ -54,6 +55,11 @@ For more control, use \code{\link[=facet_rect]{facet_rect()}} or \code{\link[=fa
 of marks. A convenient alternative to calling
 \code{style_mark(fillOpacity = ..., strokeOpacity = ...)}. Inspired by
 tinyplot's \code{alpha} argument.}
+
+\item{palette}{Character string naming a color palette (e.g.,
+\code{'category10'}, \code{'tableau10'}, \code{'set2'}). A convenient alternative to
+calling \code{scale_color(palette = ...)}. Inspired by tinyplot's \code{palette}
+argument.}
 }
 \description{
 \code{gg()} is a convenient shorthand for \code{\link[=g2]{g2()}}, inspired by tinyplot's \code{plt()}
diff --git a/tests/testit/test-gglite.R b/tests/testit/test-gglite.R
index a4c70d8..f29db06 100644
--- a/tests/testit/test-gglite.R
+++ b/tests/testit/test-gglite.R
@@ -138,3 +138,8 @@ assert('g2() by argument sets color aesthetic', {
   chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', by = 'Species')
   (chart$aesthetics$color %==% 'Species')
 })
+
+assert('g2() palette argument sets color scale palette', {
+  chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', palette = 'set2')
+  (chart$scales$color$palette %==% 'set2')
+})

From c67c1886780c617fe3c44e4fb0f7072038842bdd Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 06:47:07 +0000
Subject: [PATCH 07/12] Update NEWS.md with tinyplot-inspired features

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/df53ceb6-3fa6-43d1-aba3-b50da99ad847

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 NEWS.md | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index 0624123..2d0801f 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -7,3 +7,31 @@ with support for 35+ geometry types (marks), scales, coordinates, themes,
 transforms, facets, animations, and chart components (axes, legends, titles,
 tooltips, labels, sliders, and scrollbars). Renders in R Markdown, litedown,
 Shiny, and standalone HTML previews.
+
+## Ergonomic improvements inspired by [tinyplot](https://grantmcdermott.com/tinyplot/)
+
+- Added `gg()` as a shorthand alias for `g2()`, similar to tinyplot's `plt()`
+  alias for `tinyplot()`.
+
+- Added `main` and `sub` arguments to `g2()` for setting the chart title and
+  subtitle directly, like base `plot()` and tinyplot.
+
+- Added `by` argument to `g2()` for color grouping, inspired by tinyplot's `by`
+  argument. Equivalent to `color = 'column'`.
+
+- **Breaking change:** The formula `|` operator now sets color grouping (e.g.,
+  `y ~ x | Species` maps `Species` to color) instead of faceting. This aligns
+  with tinyplot's formula convention, where `|` means "group by." Faceting is
+  now done via the new `facet` argument.
+
+- Added `facet` argument to `g2()` accepting a formula (`~ z` for columns,
+  `y ~ x` for grid) or a character string. Inspired by tinyplot's `facet`
+  argument.
+
+- Added `alpha` argument to `g2()` for controlling mark opacity, inspired by
+  tinyplot's `alpha` argument. Sets `fillOpacity` and `strokeOpacity` on all
+  marks without needing `style_mark()`.
+
+- Added `palette` argument to `g2()` for convenient color palette selection
+  (e.g., `palette = 'set2'`), inspired by tinyplot's `palette` argument.
+  Equivalent to `scale_color(palette = ...)`.

From f206bf9d2037592a5339c5d99678dfb5a0d12bd7 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 06:48:42 +0000
Subject: [PATCH 08/12] Address code review: fix alpha null style, simplify by
 logic, enhance gg() test

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/df53ceb6-3fa6-43d1-aba3-b50da99ad847

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 R/gglite.R                 | 2 +-
 R/render.R                 | 3 ++-
 tests/testit/test-gglite.R | 6 ++++++
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/R/gglite.R b/R/gglite.R
index 4b5e4d6..86625bf 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -163,7 +163,7 @@ g2 = function(
   ), class = 'g2')
   if (length(dots)) chart$aesthetics = modifyList(chart$aesthetics, dots)
   # by argument (explicit or from formula |) sets color grouping
-  if (is.null(by) && !is.null(by_from_formula)) by = by_from_formula
+  if (is.null(by)) by = by_from_formula
   if (!is.null(by)) chart$aesthetics$color = by
   if (!is.null(palette)) chart$scales$color = list(palette = palette)
   chart
diff --git a/R/render.R b/R/render.R
index 91c5dc5..9965ecb 100644
--- a/R/render.R
+++ b/R/render.R
@@ -101,7 +101,8 @@ build_config = function(chart) {
   if (!is.null(chart$alpha)) {
     a = chart$alpha
     for (i in seq_along(config$children)) {
-      s = config$children[[i]]$style
+      s = if (is.null(config$children[[i]]$style)) list() else
+        config$children[[i]]$style
       if (is.null(s$fillOpacity)) s$fillOpacity = a
       if (is.null(s$strokeOpacity)) s$strokeOpacity = a
       config$children[[i]]$style = s
diff --git a/tests/testit/test-gglite.R b/tests/testit/test-gglite.R
index f29db06..7c65c1f 100644
--- a/tests/testit/test-gglite.R
+++ b/tests/testit/test-gglite.R
@@ -121,6 +121,12 @@ assert('gg() is a shorthand alias for g2()', {
   (inherits(chart, 'g2'))
   (chart$aesthetics$x %==% 'mpg')
   (chart$aesthetics$y %==% 'hp')
+  # gg() passes through all parameters
+  chart2 = gg(iris, Sepal.Length ~ Sepal.Width, by = 'Species',
+    main = 'Test', alpha = 0.5)
+  (chart2$aesthetics$color %==% 'Species')
+  (chart2$chart_title %==% 'Test')
+  (chart2$alpha %==% 0.5)
 })
 
 assert('g2() main argument sets chart title', {

From 2ed6e9b20b2fe43f8311969eda2ff311a79c46d1 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 07:02:41 +0000
Subject: [PATCH 09/12] Keep only title/subtitle; drop gg(), by, |color, alpha,
 palette, facet per review

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/2d28c2bc-b9d1-4f63-b367-28a0353f740a

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 NAMESPACE                  |  1 -
 NEWS.md                    | 29 +------------
 R/gglite.R                 | 86 +++++++-------------------------------
 R/render.R                 | 12 ------
 R/utils.R                  | 17 ++++++--
 man/g2.Rd                  | 58 +++++--------------------
 man/gg.Rd                  | 70 -------------------------------
 tests/testit/test-gglite.R | 56 +++++--------------------
 tests/testit/test-render.R | 15 -------
 tests/testit/test-utils.R  | 12 +++---
 vignettes/gglite.Rmd       |  8 +---
 11 files changed, 58 insertions(+), 306 deletions(-)
 delete mode 100644 man/gg.Rd

diff --git a/NAMESPACE b/NAMESPACE
index 305571a..a4c897f 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -20,7 +20,6 @@ export(facet_circle)
 export(facet_rect)
 export(g2)
 export(g2Output)
-export(gg)
 export(interact)
 export(labels_)
 export(legend_)
diff --git a/NEWS.md b/NEWS.md
index 2d0801f..662483e 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -8,30 +8,5 @@ transforms, facets, animations, and chart components (axes, legends, titles,
 tooltips, labels, sliders, and scrollbars). Renders in R Markdown, litedown,
 Shiny, and standalone HTML previews.
 
-## Ergonomic improvements inspired by [tinyplot](https://grantmcdermott.com/tinyplot/)
-
-- Added `gg()` as a shorthand alias for `g2()`, similar to tinyplot's `plt()`
-  alias for `tinyplot()`.
-
-- Added `main` and `sub` arguments to `g2()` for setting the chart title and
-  subtitle directly, like base `plot()` and tinyplot.
-
-- Added `by` argument to `g2()` for color grouping, inspired by tinyplot's `by`
-  argument. Equivalent to `color = 'column'`.
-
-- **Breaking change:** The formula `|` operator now sets color grouping (e.g.,
-  `y ~ x | Species` maps `Species` to color) instead of faceting. This aligns
-  with tinyplot's formula convention, where `|` means "group by." Faceting is
-  now done via the new `facet` argument.
-
-- Added `facet` argument to `g2()` accepting a formula (`~ z` for columns,
-  `y ~ x` for grid) or a character string. Inspired by tinyplot's `facet`
-  argument.
-
-- Added `alpha` argument to `g2()` for controlling mark opacity, inspired by
-  tinyplot's `alpha` argument. Sets `fillOpacity` and `strokeOpacity` on all
-  marks without needing `style_mark()`.
-
-- Added `palette` argument to `g2()` for convenient color palette selection
-  (e.g., `palette = 'set2'`), inspired by tinyplot's `palette` argument.
-  Equivalent to `scale_color(palette = ...)`.
+- Added `title` and `subtitle` arguments to `g2()` for setting the chart title
+  and subtitle directly, as a convenient alternative to piping into `title_()`.
diff --git a/R/gglite.R b/R/gglite.R
index 86625bf..3e6a229 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -34,8 +34,8 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'   \item{`~ x`}{Maps only `x` (e.g., for histograms or bar counts).}
 #'   \item{`~ x1 + x2 + x3`}{Creates a `position` encoding with multiple
 #'     fields (for parallel coordinates).}
-#'   \item{`y ~ x | z`}{Groups by `z` (maps to color), inspired by
-#'     tinyplot's formula convention.}
+#'   \item{`y ~ x | z`}{Facets the chart by `z` (column direction).}
+#'   \item{`y ~ x | z1 + z2`}{Facets by `z1` (columns) and `z2` (rows).}
 #' }
 #' Additional aesthetics (e.g., `color`, `size`) can still be passed as named
 #' arguments alongside the formula.
@@ -52,24 +52,10 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'   (applied to all sides) or a length-4 vector `c(top, right, bottom, left)`;
 #'   use `NA` to skip individual sides. `NULL` (the default) leaves the value
 #'   unset.
-#' @param main Chart title string, a convenient alternative to calling
-#'   [title_()] separately (inspired by base [plot()] and tinyplot).
-#' @param sub Chart subtitle string. Only used when `main` is also provided.
-#' @param by Column name (character string) to group the data by color,
-#'   inspired by tinyplot's `by` argument. Equivalent to passing
-#'   `color = 'column'`.
-#' @param facet Faceting specification: a one-sided formula (`~ z` for
-#'   column faceting, `y ~ x` for grid faceting), or a character string
-#'   naming the faceting variable. Inspired by tinyplot's `facet` argument.
-#'   For more control, use [facet_rect()] or [facet_circle()] instead.
-#' @param alpha Numeric in `[0, 1]` controlling the fill and stroke opacity
-#'   of marks. A convenient alternative to calling
-#'   `style_mark(fillOpacity = ..., strokeOpacity = ...)`. Inspired by
-#'   tinyplot's `alpha` argument.
-#' @param palette Character string naming a color palette (e.g.,
-#'   `'category10'`, `'tableau10'`, `'set2'`). A convenient alternative to
-#'   calling `scale_color(palette = ...)`. Inspired by tinyplot's `palette`
-#'   argument.
+#' @param title Chart title string, a convenient alternative to piping into
+#'   [title_()] separately.
+#' @param subtitle Chart subtitle string. Only used when `title` is also
+#'   provided.
 #' @return A `g2` object (S3 class).
 #' @import stats utils
 #' @export
@@ -85,48 +71,19 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #' g2(sunspot.year)
 #' g2(EuStockMarkets)
 #'
-#' # Title and subtitle (like base plot's main/sub)
-#' g2(mtcars, hp ~ mpg, main = 'Motor Trend Cars', sub = 'mpg vs hp')
-#'
-#' # Grouping by color (like tinyplot's by argument)
-#' g2(iris, Sepal.Length ~ Sepal.Width, by = 'Species')
-#'
-#' # Formula | for color grouping (tinyplot convention)
-#' g2(iris, Sepal.Length ~ Sepal.Width | Species)
-#'
-#' # Faceting via the facet argument (like tinyplot)
-#' g2(iris, Sepal.Length ~ Sepal.Width, facet = ~Species)
-#' g2(mtcars, hp ~ mpg, facet = gear ~ cyl)
-#'
-#' # Adjust opacity (like tinyplot's alpha)
-#' g2(iris, Sepal.Length ~ Sepal.Width | Species, alpha = 0.5)
-#'
-#' # Set color palette (like tinyplot's palette)
-#' g2(iris, Sepal.Length ~ Sepal.Width | Species, palette = 'set2')
+#' # Title and subtitle
+#' g2(mtcars, hp ~ mpg, title = 'Motor Trend Cars', subtitle = 'mpg vs hp')
 g2 = function(
   data = NULL, ..., width = 640, height = 480,
   padding = NULL, margin = NULL, inset = NULL,
-  main = NULL, sub = NULL, by = NULL, facet = NULL, alpha = NULL,
-  palette = NULL
+  title = NULL, subtitle = NULL
 ) {
   dots = list(...)
-  by_from_formula = NULL
   has_formula = length(dots) && inherits(dots[[1]], 'formula')
-  if (has_formula) {
+  facet_from_formula = if (has_formula) {
     parsed = parse_formula(dots[[1]])
     dots = c(parsed$aesthetics, dots[-1])
-    by_from_formula = parsed$by
-  }
-  # Build facet from the facet argument (formula or character)
-  facet_config = if (inherits(facet, 'formula')) {
-    fterms = if (length(facet) == 3) {
-      list(y = deparse(facet[[2]]), x = deparse(facet[[3]]))
-    } else {
-      list(x = deparse(facet[[2]]))
-    }
-    list(type = 'facetRect', encode = fterms)
-  } else if (is.character(facet)) {
-    list(type = 'facetRect', encode = list(x = facet))
+    parsed$facet
   }
   # Convert time series to data frame with default aesthetics
   ts_aes = NULL
@@ -150,11 +107,10 @@ g2 = function(
     theme = NULL,
     axes = list(),
     legends = list(),
-    chart_title = if (!is.null(main)) {
-      if (!is.null(sub)) list(title = main, subtitle = sub) else main
+    chart_title = if (!is.null(title)) {
+      if (!is.null(subtitle)) list(title = title, subtitle = subtitle) else title
     },
-    facet = facet_config,
-    alpha = alpha,
+    facet = facet_from_formula,
     layout = c(
       process_layout('padding', padding),
       process_layout('margin', margin),
@@ -162,10 +118,6 @@ g2 = function(
     )
   ), class = 'g2')
   if (length(dots)) chart$aesthetics = modifyList(chart$aesthetics, dots)
-  # by argument (explicit or from formula |) sets color grouping
-  if (is.null(by)) by = by_from_formula
-  if (!is.null(by)) chart$aesthetics$color = by
-  if (!is.null(palette)) chart$scales$color = list(palette = palette)
   chart
 }
 
@@ -186,14 +138,4 @@ encode = function(chart, ...) {
   chart
 }
 
-#' Shorthand Alias for [g2()]
-#'
-#' `gg()` is a convenient shorthand for [g2()], inspired by tinyplot's `plt()`
-#' alias. All arguments are passed through to [g2()].
-#'
-#' @inheritParams g2
-#' @export
-#' @examples
-#' gg(mtcars, x = 'mpg', y = 'hp')
-gg = g2
 
diff --git a/R/render.R b/R/render.R
index 9965ecb..87aad54 100644
--- a/R/render.R
+++ b/R/render.R
@@ -97,18 +97,6 @@ build_config = function(chart) {
 
   if (length(marks)) config$children = marks
 
-  # Apply chart-level alpha to all marks
-  if (!is.null(chart$alpha)) {
-    a = chart$alpha
-    for (i in seq_along(config$children)) {
-      s = if (is.null(config$children[[i]]$style)) list() else
-        config$children[[i]]$style
-      if (is.null(s$fillOpacity)) s$fillOpacity = a
-      if (is.null(s$strokeOpacity)) s$strokeOpacity = a
-      config$children[[i]]$style = s
-    }
-  }
-
   # Chart-wide config
   if (length(chart$scales)) config$scale = chart$scales
   if (!is.null(chart$coords)) config$coordinate = chart$coords
diff --git a/R/utils.R b/R/utils.R
index bce5778..14289f8 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -129,10 +129,10 @@ parse_formula = function(f) {
   lhs = if (length(f) == 3) f[[2]]
   rhs = if (length(f) == 3) f[[3]] else f[[2]]
 
-  # Extract conditioning (by/color) variable from |
-  by_term = NULL
+  # Extract conditioning (facet) variables from |
+  facet_terms = NULL
   if (is.call(rhs) && identical(rhs[[1]], as.name('|'))) {
-    by_term = deparse(rhs[[3]])
+    facet_terms = extract_terms(rhs[[3]])
     rhs = rhs[[2]]
   }
 
@@ -147,5 +147,14 @@ parse_formula = function(f) {
     aesthetics$position = rhs_terms
   }
 
-  list(aesthetics = aesthetics, by = by_term)
+  # Build facet
+  facet = NULL
+  if (length(facet_terms)) {
+    enc = list()
+    if (length(facet_terms) >= 1) enc$x = facet_terms[1]
+    if (length(facet_terms) >= 2) enc$y = facet_terms[2]
+    facet = list(type = 'facetRect', encode = enc)
+  }
+
+  list(aesthetics = aesthetics, facet = facet)
 }
diff --git a/man/g2.Rd b/man/g2.Rd
index 37aa04c..cec2db1 100644
--- a/man/g2.Rd
+++ b/man/g2.Rd
@@ -12,12 +12,8 @@ g2(
   padding = NULL,
   margin = NULL,
   inset = NULL,
-  main = NULL,
-  sub = NULL,
-  by = NULL,
-  facet = NULL,
-  alpha = NULL,
-  palette = NULL
+  title = NULL,
+  subtitle = NULL
 )
 }
 \arguments{
@@ -37,29 +33,11 @@ or a formula followed by optional named aesthetics.}
 use \code{NA} to skip individual sides. \code{NULL} (the default) leaves the value
 unset.}
 
-\item{main}{Chart title string, a convenient alternative to calling
-\code{\link[=title_]{title_()}} separately (inspired by base \code{\link[=plot]{plot()}} and tinyplot).}
+\item{title}{Chart title string, a convenient alternative to piping into
+\code{\link[=title_]{title_()}} separately.}
 
-\item{sub}{Chart subtitle string. Only used when \code{main} is also provided.}
-
-\item{by}{Column name (character string) to group the data by color,
-inspired by tinyplot's \code{by} argument. Equivalent to passing
-\code{color = 'column'}.}
-
-\item{facet}{Faceting specification: a one-sided formula (\code{~ z} for
-column faceting, \code{y ~ x} for grid faceting), or a character string
-naming the faceting variable. Inspired by tinyplot's \code{facet} argument.
-For more control, use \code{\link[=facet_rect]{facet_rect()}} or \code{\link[=facet_circle]{facet_circle()}} instead.}
-
-\item{alpha}{Numeric in \verb{[0, 1]} controlling the fill and stroke opacity
-of marks. A convenient alternative to calling
-\code{style_mark(fillOpacity = ..., strokeOpacity = ...)}. Inspired by
-tinyplot's \code{alpha} argument.}
-
-\item{palette}{Character string naming a color palette (e.g.,
-\code{'category10'}, \code{'tableau10'}, \code{'set2'}). A convenient alternative to
-calling \code{scale_color(palette = ...)}. Inspired by tinyplot's \code{palette}
-argument.}
+\item{subtitle}{Chart subtitle string. Only used when \code{title} is also
+provided.}
 }
 \value{
 A \code{g2} object (S3 class).
@@ -78,8 +56,8 @@ argument after \code{data}:
 \item{\code{~ x}}{Maps only \code{x} (e.g., for histograms or bar counts).}
 \item{\code{~ x1 + x2 + x3}}{Creates a \code{position} encoding with multiple
 fields (for parallel coordinates).}
-\item{\code{y ~ x | z}}{Groups by \code{z} (maps to color), inspired by
-tinyplot's formula convention.}
+\item{\code{y ~ x | z}}{Facets the chart by \code{z} (column direction).}
+\item{\code{y ~ x | z1 + z2}}{Facets by \code{z1} (columns) and \code{z2} (rows).}
 }
 Additional aesthetics (e.g., \code{color}, \code{size}) can still be passed as named
 arguments alongside the formula.
@@ -97,22 +75,6 @@ g2(mtcars, ~ mpg)
 g2(sunspot.year)
 g2(EuStockMarkets)
 
-# Title and subtitle (like base plot's main/sub)
-g2(mtcars, hp ~ mpg, main = 'Motor Trend Cars', sub = 'mpg vs hp')
-
-# Grouping by color (like tinyplot's by argument)
-g2(iris, Sepal.Length ~ Sepal.Width, by = 'Species')
-
-# Formula | for color grouping (tinyplot convention)
-g2(iris, Sepal.Length ~ Sepal.Width | Species)
-
-# Faceting via the facet argument (like tinyplot)
-g2(iris, Sepal.Length ~ Sepal.Width, facet = ~Species)
-g2(mtcars, hp ~ mpg, facet = gear ~ cyl)
-
-# Adjust opacity (like tinyplot's alpha)
-g2(iris, Sepal.Length ~ Sepal.Width | Species, alpha = 0.5)
-
-# Set color palette (like tinyplot's palette)
-g2(iris, Sepal.Length ~ Sepal.Width | Species, palette = 'set2')
+# Title and subtitle
+g2(mtcars, hp ~ mpg, title = 'Motor Trend Cars', subtitle = 'mpg vs hp')
 }
diff --git a/man/gg.Rd b/man/gg.Rd
deleted file mode 100644
index 728b3a9..0000000
--- a/man/gg.Rd
+++ /dev/null
@@ -1,70 +0,0 @@
-% Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/gglite.R
-\name{gg}
-\alias{gg}
-\title{Shorthand Alias for \code{\link[=g2]{g2()}}}
-\usage{
-gg(
-  data = NULL,
-  ...,
-  width = 640,
-  height = 480,
-  padding = NULL,
-  margin = NULL,
-  inset = NULL,
-  main = NULL,
-  sub = NULL,
-  by = NULL,
-  facet = NULL,
-  alpha = NULL,
-  palette = NULL
-)
-}
-\arguments{
-\item{data}{A data frame, a \code{ts}/\code{mts} time series object, or \code{NULL}. Time
-series objects are automatically converted to data frames (with columns
-\code{time} and \code{value} for univariate series, or \code{time}, \code{series}, and \code{value}
-for multivariate series) and default aesthetic mappings are set
-accordingly.}
-
-\item{...}{Aesthetic mappings as \code{name = 'column'} pairs (character strings),
-or a formula followed by optional named aesthetics.}
-
-\item{width, height}{Width and height of the chart in pixels.}
-
-\item{padding, margin, inset}{Layout spacing in pixels. Each can be a scalar
-(applied to all sides) or a length-4 vector \code{c(top, right, bottom, left)};
-use \code{NA} to skip individual sides. \code{NULL} (the default) leaves the value
-unset.}
-
-\item{main}{Chart title string, a convenient alternative to calling
-\code{\link[=title_]{title_()}} separately (inspired by base \code{\link[=plot]{plot()}} and tinyplot).}
-
-\item{sub}{Chart subtitle string. Only used when \code{main} is also provided.}
-
-\item{by}{Column name (character string) to group the data by color,
-inspired by tinyplot's \code{by} argument. Equivalent to passing
-\code{color = 'column'}.}
-
-\item{facet}{Faceting specification: a one-sided formula (\code{~ z} for
-column faceting, \code{y ~ x} for grid faceting), or a character string
-naming the faceting variable. Inspired by tinyplot's \code{facet} argument.
-For more control, use \code{\link[=facet_rect]{facet_rect()}} or \code{\link[=facet_circle]{facet_circle()}} instead.}
-
-\item{alpha}{Numeric in \verb{[0, 1]} controlling the fill and stroke opacity
-of marks. A convenient alternative to calling
-\code{style_mark(fillOpacity = ..., strokeOpacity = ...)}. Inspired by
-tinyplot's \code{alpha} argument.}
-
-\item{palette}{Character string naming a color palette (e.g.,
-\code{'category10'}, \code{'tableau10'}, \code{'set2'}). A convenient alternative to
-calling \code{scale_color(palette = ...)}. Inspired by tinyplot's \code{palette}
-argument.}
-}
-\description{
-\code{gg()} is a convenient shorthand for \code{\link[=g2]{g2()}}, inspired by tinyplot's \code{plt()}
-alias. All arguments are passed through to \code{\link[=g2]{g2()}}.
-}
-\examples{
-gg(mtcars, x = 'mpg', y = 'hp')
-}
diff --git a/tests/testit/test-gglite.R b/tests/testit/test-gglite.R
index 7c65c1f..cd84008 100644
--- a/tests/testit/test-gglite.R
+++ b/tests/testit/test-gglite.R
@@ -82,31 +82,19 @@ assert('g2() formula with extra aesthetics', {
   (chart$aesthetics$color %==% 'Species')
 })
 
-assert('g2() formula with | sets color grouping (tinyplot convention)', {
+assert('g2() formula with faceting y ~ x | z', {
   chart = g2(iris, Sepal.Length ~ Sepal.Width | Species)
   (chart$aesthetics$x %==% 'Sepal.Width')
   (chart$aesthetics$y %==% 'Sepal.Length')
-  (chart$aesthetics$color %==% 'Species')
-  (is.null(chart$facet))
-})
-
-assert('g2() facet argument with one-sided formula', {
-  chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', facet = ~Species)
   (chart$facet$type %==% 'facetRect')
   (chart$facet$encode$x %==% 'Species')
 })
 
-assert('g2() facet argument with two-sided formula', {
-  chart = g2(mtcars, x = 'mpg', y = 'hp', facet = gear ~ cyl)
-  (chart$facet$type %==% 'facetRect')
-  (chart$facet$encode$x %==% 'cyl')
-  (chart$facet$encode$y %==% 'gear')
-})
-
-assert('g2() facet argument with character string', {
-  chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', facet = 'Species')
-  (chart$facet$type %==% 'facetRect')
-  (chart$facet$encode$x %==% 'Species')
+assert('g2() formula with two facet variables', {
+  df = data.frame(x = 1, y = 2, a = 'A', b = 'B')
+  chart = g2(df, y ~ x | a + b)
+  (chart$facet$encode$x %==% 'a')
+  (chart$facet$encode$y %==% 'b')
 })
 
 assert('g2() formula ~ x1 + x2 + x3 sets position encoding', {
@@ -116,36 +104,14 @@ assert('g2() formula ~ x1 + x2 + x3 sets position encoding', {
   (is.null(chart$aesthetics$x))
 })
 
-assert('gg() is a shorthand alias for g2()', {
-  chart = gg(mtcars, x = 'mpg', y = 'hp')
-  (inherits(chart, 'g2'))
-  (chart$aesthetics$x %==% 'mpg')
-  (chart$aesthetics$y %==% 'hp')
-  # gg() passes through all parameters
-  chart2 = gg(iris, Sepal.Length ~ Sepal.Width, by = 'Species',
-    main = 'Test', alpha = 0.5)
-  (chart2$aesthetics$color %==% 'Species')
-  (chart2$chart_title %==% 'Test')
-  (chart2$alpha %==% 0.5)
-})
-
-assert('g2() main argument sets chart title', {
-  chart = g2(mtcars, x = 'mpg', y = 'hp', main = 'My Title')
+assert('g2() title argument sets chart title', {
+  chart = g2(mtcars, x = 'mpg', y = 'hp', title = 'My Title')
   (chart$chart_title %==% 'My Title')
 })
 
-assert('g2() main and sub arguments set title and subtitle', {
-  chart = g2(mtcars, x = 'mpg', y = 'hp', main = 'Title', sub = 'Subtitle')
+assert('g2() title and subtitle arguments set title and subtitle', {
+  chart = g2(mtcars, x = 'mpg', y = 'hp',
+    title = 'Title', subtitle = 'Subtitle')
   (chart$chart_title$title %==% 'Title')
   (chart$chart_title$subtitle %==% 'Subtitle')
 })
-
-assert('g2() by argument sets color aesthetic', {
-  chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', by = 'Species')
-  (chart$aesthetics$color %==% 'Species')
-})
-
-assert('g2() palette argument sets color scale palette', {
-  chart = g2(iris, x = 'Sepal.Width', y = 'Sepal.Length', palette = 'set2')
-  (chart$scales$color$palette %==% 'set2')
-})
diff --git a/tests/testit/test-render.R b/tests/testit/test-render.R
index e1c44b1..d437869 100644
--- a/tests/testit/test-render.R
+++ b/tests/testit/test-render.R
@@ -215,18 +215,3 @@ assert('build_config ts y-axis title does not override user title', {
   config = build_config(chart)
   (config$axis$y$title %==% 'My Title')
 })
-
-assert('build_config applies alpha to mark styles', {
-  chart = g2(mtcars, x = 'mpg', y = 'hp', alpha = 0.3) |> mark_point()
-  config = build_config(chart)
-  (config$children[[1]]$style$fillOpacity %==% 0.3)
-  (config$children[[1]]$style$strokeOpacity %==% 0.3)
-})
-
-assert('build_config alpha does not override explicit mark style opacity', {
-  chart = g2(mtcars, x = 'mpg', y = 'hp', alpha = 0.3) |>
-    mark_point() |> style_mark(fillOpacity = 0.8)
-  config = build_config(chart)
-  (config$children[[1]]$style$fillOpacity %==% 0.8)
-  (config$children[[1]]$style$strokeOpacity %==% 0.3)
-})
diff --git a/tests/testit/test-utils.R b/tests/testit/test-utils.R
index da0f4b4..55428e1 100644
--- a/tests/testit/test-utils.R
+++ b/tests/testit/test-utils.R
@@ -54,16 +54,18 @@ assert('parse_formula: ~ x1 + x2 + x3', {
   (is.null(res$aesthetics$x))
 })
 
-assert('parse_formula: y ~ x | z sets color grouping (not facet)', {
+assert('parse_formula: y ~ x | z', {
   res = parse_formula(hp ~ mpg | cyl)
   (res$aesthetics$x %==% 'mpg')
   (res$aesthetics$y %==% 'hp')
-  (res$by %==% 'cyl')
+  (res$facet$type %==% 'facetRect')
+  (res$facet$encode$x %==% 'cyl')
 })
 
-assert('parse_formula: no | returns NULL by', {
-  res = parse_formula(y ~ x)
-  (is.null(res$by))
+assert('parse_formula: y ~ x | z1 + z2', {
+  res = parse_formula(y ~ x | a + b)
+  (res$facet$encode$x %==% 'a')
+  (res$facet$encode$y %==% 'b')
 })
 
 assert('ts_to_df converts univariate ts', {
diff --git a/vignettes/gglite.Rmd b/vignettes/gglite.Rmd
index 0197bfe..8011024 100644
--- a/vignettes/gglite.Rmd
+++ b/vignettes/gglite.Rmd
@@ -67,18 +67,12 @@ Additional aesthetics like `color` can be passed alongside the formula:
 g2(iris, Sepal.Length ~ Sepal.Width, color = 'Species')
 ```
 
-Use `|` for color grouping (inspired by tinyplot):
+Use `|` for faceting:
 
 ```{r}
 g2(iris, Sepal.Length ~ Sepal.Width | Species)
 ```
 
-Use the `facet` argument for faceting (also inspired by tinyplot):
-
-```{r}
-g2(iris, Sepal.Length ~ Sepal.Width, facet = ~Species)
-```
-
 A one-sided formula maps only `x` (useful for histograms or counts):
 
 ```{r}

From 1c4c63a502d36878bab30239167b31d481c5f37b Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 07:21:20 +0000
Subject: [PATCH 10/12] Simplify chart_title, remove is.null() checks in
 build_config, drop NEWS for v0.1

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/1f1ea7ca-8cdb-4cc9-9f6f-5bfbe65344d2

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 .github/copilot-instructions.md | 17 ++++++++++-------
 NEWS.md                         |  3 ---
 R/gglite.R                      |  7 ++-----
 R/render.R                      |  8 ++++----
 man/g2.Rd                       |  3 +--
 tests/testit/test-gglite.R      |  2 +-
 6 files changed, 18 insertions(+), 22 deletions(-)

diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index cdcc6a6..7ae5734 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -155,7 +155,9 @@ Before submitting changes:
 2. Run `R CMD check gglite_*.tar.gz --no-manual` to validate
 3. Ensure all tests pass: `Rscript tests/test-all.R`
 4. Check GitHub Actions status for multi-platform validation
-5. Update `NEWS.md` to document your changes (except for v0.1)
+5. Update `NEWS.md` to document your changes (except for v0.1). **Do NOT add
+   NEWS entries while the package is still at v0.1** — the initial release
+   description is sufficient.
 
 ## Important Conventions
 
@@ -220,12 +222,13 @@ as character strings, e.g., `g2(mtcars, x = 'mpg', y = 'hp')`.
    especially automatically generated ones.
 8. **Testing**: Use testit assertions with proper error handling
 9. **Update NEWS.md**: When making changes, make sure to update `NEWS.md`
-   accordingly to document what changed. The first heading in NEWS.md always
-   represents the dev version and must be of the form `# PKG x.y` where PKG
-   is the package name and x.y is the next version to be released to CRAN
-   (note: x.y, not x.y.0). Usually y is bumped from the current minor
-   version, e.g., if the current dev version is 1.8.3, the next CRAN release
-   is expected to be 1.9.
+   accordingly to document what changed — **except for v0.1** (do NOT add
+   individual change entries for the initial release). The first heading in
+   NEWS.md always represents the dev version and must be of the form
+   `# PKG x.y` where PKG is the package name and x.y is the next version to
+   be released to CRAN (note: x.y, not x.y.0). Usually y is bumped from the
+   current minor version, e.g., if the current dev version is 1.8.3, the next
+   CRAN release is expected to be 1.9.
 
 ## Package API
 
diff --git a/NEWS.md b/NEWS.md
index 662483e..0624123 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -7,6 +7,3 @@ with support for 35+ geometry types (marks), scales, coordinates, themes,
 transforms, facets, animations, and chart components (axes, legends, titles,
 tooltips, labels, sliders, and scrollbars). Renders in R Markdown, litedown,
 Shiny, and standalone HTML previews.
-
-- Added `title` and `subtitle` arguments to `g2()` for setting the chart title
-  and subtitle directly, as a convenient alternative to piping into `title_()`.
diff --git a/R/gglite.R b/R/gglite.R
index 3e6a229..6ea3c79 100644
--- a/R/gglite.R
+++ b/R/gglite.R
@@ -54,8 +54,7 @@ g2_patches_cdn = 'https://cdn.jsdelivr.net/npm/@xiee/utils@v1.14.30/js/g2-patche
 #'   unset.
 #' @param title Chart title string, a convenient alternative to piping into
 #'   [title_()] separately.
-#' @param subtitle Chart subtitle string. Only used when `title` is also
-#'   provided.
+#' @param subtitle Chart subtitle string.
 #' @return A `g2` object (S3 class).
 #' @import stats utils
 #' @export
@@ -107,9 +106,7 @@ g2 = function(
     theme = NULL,
     axes = list(),
     legends = list(),
-    chart_title = if (!is.null(title)) {
-      if (!is.null(subtitle)) list(title = title, subtitle = subtitle) else title
-    },
+    chart_title = dropNulls(list(title = title, subtitle = subtitle)),
     facet = facet_from_formula,
     layout = c(
       process_layout('padding', padding),
diff --git a/R/render.R b/R/render.R
index 87aad54..7fcdfca 100644
--- a/R/render.R
+++ b/R/render.R
@@ -109,10 +109,10 @@ build_config = function(chart) {
       config$axis$y = modifyList(as.list(y_ax), list(title = chart$ts_name))
   }
   if (length(chart$legends)) config$legend = chart$legends
-  if (!is.null(chart$chart_title)) config$title = chart$chart_title
-  if (!is.null(chart$tooltip_config)) config$tooltip = chart$tooltip_config
-  if (!is.null(chart$sliders)) config$slider = chart$sliders
-  if (!is.null(chart$scrollbars)) config$scrollbar = chart$scrollbars
+  if (length(chart$chart_title)) config$title = chart$chart_title
+  config$tooltip = chart$tooltip_config
+  config$slider = chart$sliders
+  config$scrollbar = chart$scrollbars
   if (length(chart$layout)) config = modifyList(config, chart$layout)
 
   # Theme: merge global option with per-chart theme
diff --git a/man/g2.Rd b/man/g2.Rd
index cec2db1..d1692e8 100644
--- a/man/g2.Rd
+++ b/man/g2.Rd
@@ -36,8 +36,7 @@ unset.}
 \item{title}{Chart title string, a convenient alternative to piping into
 \code{\link[=title_]{title_()}} separately.}
 
-\item{subtitle}{Chart subtitle string. Only used when \code{title} is also
-provided.}
+\item{subtitle}{Chart subtitle string.}
 }
 \value{
 A \code{g2} object (S3 class).
diff --git a/tests/testit/test-gglite.R b/tests/testit/test-gglite.R
index cd84008..0fe2564 100644
--- a/tests/testit/test-gglite.R
+++ b/tests/testit/test-gglite.R
@@ -106,7 +106,7 @@ assert('g2() formula ~ x1 + x2 + x3 sets position encoding', {
 
 assert('g2() title argument sets chart title', {
   chart = g2(mtcars, x = 'mpg', y = 'hp', title = 'My Title')
-  (chart$chart_title %==% 'My Title')
+  (chart$chart_title$title %==% 'My Title')
 })
 
 assert('g2() title and subtitle arguments set title and subtitle', {

From 42c2a3b0ae8c6eee5cf45659de93f57504774b6c Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 2 Apr 2026 07:35:32 +0000
Subject: [PATCH 11/12] Add title/subtitle g2() param examples to
 titles-tooltips.Rmd

Agent-Logs-Url: https://github.com/yihui/gglite/sessions/c1c083a1-cad5-4057-a1c8-81d37f9f548b

Co-authored-by: yihui-bot <264330240+yihui-bot@users.noreply.github.com>
---
 examples/titles-tooltips.Rmd | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/examples/titles-tooltips.Rmd b/examples/titles-tooltips.Rmd
index 7204c80..1fe41cb 100644
--- a/examples/titles-tooltips.Rmd
+++ b/examples/titles-tooltips.Rmd
@@ -8,6 +8,19 @@ library(gglite)
 
 ## Chart Title
 
+### Title via `g2()` arguments
+
+```{r}
+g2(mtcars, x = 'mpg', y = 'hp', title = 'Motor Trend Cars')
+```
+
+### Title and subtitle via `g2()` arguments
+
+```{r}
+g2(mtcars, x = 'mpg', y = 'hp',
+  title = 'Motor Trend Cars', subtitle = 'mpg vs horsepower')
+```
+
 ### Simple title
 
 ```{r}

From 05c16fe3bb4e8e05889d6c7fa549bf779f7bdf65 Mon Sep 17 00:00:00 2001
From: Yihui bot <yihui.xie@cos.name>
Date: Thu, 2 Apr 2026 02:37:04 -0500
Subject: [PATCH 12/12] Remove title example from titles-tooltips.Rmd

---
 examples/titles-tooltips.Rmd | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/examples/titles-tooltips.Rmd b/examples/titles-tooltips.Rmd
index 1fe41cb..70a5230 100644
--- a/examples/titles-tooltips.Rmd
+++ b/examples/titles-tooltips.Rmd
@@ -8,12 +8,6 @@ library(gglite)
 
 ## Chart Title
 
-### Title via `g2()` arguments
-
-```{r}
-g2(mtcars, x = 'mpg', y = 'hp', title = 'Motor Trend Cars')
-```
-
 ### Title and subtitle via `g2()` arguments
 
 ```{r}