Handle brms 0 + Intercept formulas in get_modelmatrix() (#1199)

* Initial plan

* Fix brms get_modelmatrix Intercept handling

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Co-authored-by: DominiqueMakowski <8875533+DominiqueMakowski@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: DominiqueMakowski <8875533+DominiqueMakowski@users.noreply.github.com>

Author: Copilot

DESCRIPTION

@@ -1,7 +1,7 @@
 Type: Package
 Package: insight
 Title: Easy Access to Model Information for Various Model Objects
-Version: 1.5.1.1
+Version: 1.5.1.2
 Authors@R:
     c(person(given = "Daniel",
              family = "Lüdecke",

NEWS.md

@@ -5,6 +5,11 @@
 * Major performance improvement for `compact_list` on very large, nested list
   objects.
 
+## Bug fixes
+
+* `get_modelmatrix()` now correctly handles *brms* models fitted with
+  `0 + Intercept` formulas.
+
 # insight 1.5.1
 
 ## Changes

R/get_modelmatrix.R

@@ -178,24 +178,33 @@ get_modelmatrix.svysurvreg <- get_modelmatrix.svyglm
 
 #' @export
 get_modelmatrix.brmsfit <- function(x, ...) {
-  formula_rhs <- safe_deparse(find_formula(x, verbose = FALSE)$conditional[[3]])
+  conditional_formula <- find_formula(x, verbose = FALSE)$conditional
+  formula_rhs <- safe_deparse(conditional_formula[[3]])
+  model_data <- get_data(x, verbose = FALSE)
   # exception: for null-models, we need different handling, else `reformulate()`
   # will not work.
   if (identical(formula_rhs, "1")) {
-    mm <- get_data(x, verbose = FALSE)
-    mm[[1]] <- 1
-    colnames(mm)[1] <- "(Intercept)"
-    as.matrix(mm[1])
+    matrix(1, nrow = nrow(model_data), dimnames = list(NULL, "(Intercept)"))
   } else {
     formula_rhs <- stats::as.formula(paste0("~", formula_rhs))
+    intercept <- has_intercept(x, verbose = FALSE)
+    predictors <- setdiff(all.vars(formula_rhs), "Intercept")
     # the formula used in model.matrix() is not allowed to have special functions,
     # like brms::mo() and similar. Thus, we reformulate after using "all.vars()",
     # which will only keep the variable names.
-    .data_in_dots(
-      ...,
-      object = stats::reformulate(all.vars(formula_rhs)),
-      default_data = get_data(x, verbose = FALSE)
-    )
+    if (!length(predictors)) {
+      if (intercept) {
+        matrix(1, nrow = nrow(model_data), dimnames = list(NULL, "(Intercept)"))
+      } else {
+        matrix(nrow = nrow(model_data), ncol = 0)
+      }
+    } else {
+      .data_in_dots(
+        ...,
+        object = stats::reformulate(predictors, intercept = intercept),
+        default_data = model_data
+      )
+    }
   }
 }
 

tests/testthat/test-brms.R

@@ -1051,6 +1051,30 @@ test_that("get_modelmatrix", {
   expect_identical(dim(out), c(32L, 2L))
 })
 
+test_that("get_modelmatrix handles brms Intercept terms, Issue #1199", {
+  # apparently BH is required to fit these brms models
+  skip_if_not_installed("BH")
+  # sink() writing permission fail on some Windows CI machines
+  skip_on_os("windows")
+
+  void <- suppressMessages(suppressWarnings(capture.output({
+    mod <- brms::brm(
+      mpg ~ 0 + Intercept + wt,
+      data = mtcars,
+      refresh = 0,
+      chains = 1,
+      iter = 600,
+      warmup = 300,
+      cores = 1,
+      silent = 2
+    )
+  })))
+
+  out <- get_modelmatrix(mod)
+  expect_identical(colnames(out), c("(Intercept)", "wt"))
+  expect_identical(dim(out), c(nrow(mtcars), 2L))
+})
+
 test_that("find_variables, mo", {
   m10 <- suppressWarnings(insight::download_model("brms_lf_1"))
   expect_identical(