Add highlighting feature for data elements

altair_upset/upset.py

@@ -1,4 +1,4 @@
-from typing import List, Optional, Union
+from typing import List, Literal, Optional, Union
 
 import altair as alt
 import pandas as pd
@@ -9,6 +9,51 @@
 from .transforms import create_base_chart
 
 
+def _determine_highlighted_intersections(
+    data: pd.DataFrame,
+    highlight: Union[Literal["least", "greatest"], int, List[int]],
+) -> List[float]:
+    """Determine which intersection IDs to highlight based on the highlight parameter.
+
+    Parameters
+    ----------
+    data : pd.DataFrame
+        The preprocessed data with intersection_id and count columns
+    highlight : "least", "greatest", int, or list of int
+        The highlighting criteria
+
+    Returns
+    -------
+    list of float
+        List of intersection_ids to highlight
+    """
+    # Get unique intersections with their counts
+    intersections = (
+        data.groupby("intersection_id")["count"]
+        .first()
+        .reset_index()
+        .sort_index()
+    )
+
+    if isinstance(highlight, str):
+        if highlight == "least":
+            min_idx = intersections["count"].idxmin()
+            return [intersections.loc[min_idx, "intersection_id"]]
+        else:  # highlight == "greatest"
+            max_idx = intersections["count"].idxmax()
+            return [intersections.loc[max_idx, "intersection_id"]]
+    elif isinstance(highlight, int):
+        if highlight < len(intersections):
+            return [intersections.iloc[highlight]["intersection_id"]]
+        return []
+    else:  # isinstance(highlight, list)
+        return [
+            intersections.iloc[i]["intersection_id"]
+            for i in highlight
+            if i < len(intersections)
+        ]
+
+
 class UpSetChart:
     """A wrapper class for UpSet plots."""
 
@@ -84,6 +129,7 @@ def UpSetAltair(
         "#BDC6CA",
     ],
     highlight_color: str = "#EA4667",
+    highlight: Optional[Union[Literal["least", "greatest"], int, List[int]]] = None,
     glyph_size: int = 100,  # Reduced from 200
     set_label_bg_size: int = 500,  # Reduced from 1000
     line_connection_size: int = 1,  # Reduced from 2
@@ -130,7 +176,14 @@ def UpSetAltair(
     color_range : list of str
         List of colors for the sets. Defaults to a colorblind-friendly palette.
     highlight_color : str, default "#EA4667"
-        Color used for highlighting on hover.
+        Color used for highlighting on hover or programmatic highlighting.
+    highlight : str, int, or list of int, optional
+        Specifies which intersections to highlight programmatically:
+        - None (default): interactive hover highlighting
+        - "least": highlight the intersection with the smallest size
+        - "greatest": highlight the intersection with the largest size
+        - int: highlight the intersection at the specified index (0-based)
+        - list of int: highlight multiple intersections by their indices
     glyph_size : int, default 200
         Size of the matrix glyphs in pixels.
     set_label_bg_size : int, default 1000
@@ -200,6 +253,18 @@ def UpSetAltair(
         raise ValueError("if provided, abbre must have the same length as sets")
     if vertical_bar_y_axis_orient not in ["left", "right"]:
         raise ValueError("vertical bar y axis orient must be 'left' or 'right'")
+    if highlight is not None:
+        if isinstance(highlight, str):
+            if highlight not in ["least", "greatest"]:
+                raise ValueError("highlight string must be 'least' or 'greatest'")
+        elif isinstance(highlight, int):
+            if highlight < 0:
+                raise ValueError("highlight index must be non-negative")
+        elif isinstance(highlight, list):
+            if not all(isinstance(i, int) and i >= 0 for i in highlight):
+                raise ValueError("highlight list must contain non-negative integers")
+        else:
+            raise TypeError("highlight must be None, str, int, or list of int")
 
     # Apply theme if specified
     if theme is not None:
@@ -212,7 +277,18 @@ def UpSetAltair(
 
     # Setup selections for interactivity
     legend_selection = alt.selection_point(fields=["set"], bind="legend")
-    color_selection = alt.selection_point(fields=["intersection_id"], on="mouseover")
+
+    # Setup color selection based on highlight parameter
+    if highlight is None:
+        # Default hover behavior
+        color_selection = alt.selection_point(fields=["intersection_id"], on="mouseover")
+    else:
+        # Determine which intersections to highlight and create fixed selection
+        highlighted_ids = _determine_highlighted_intersections(data, highlight)
+        color_selection = alt.selection_point(
+            fields=["intersection_id"],
+            value=[{"intersection_id": id_} for id_ in highlighted_ids]
+        )
 
     # Calculate dimensions
     if horizontal_bar_chart_width is None:

docs/examples/advanced_features.rst

@@ -92,3 +92,75 @@ Let's analyze the engagement patterns across different platform combinations:
         print(f"Avg Time: {row['avg_time']:.1f} minutes")
         print(f"Avg Posts: {row['avg_posts']:.1f} per week")
         print(f"Avg Engagement: {row['avg_engagement']:.1f}%")
+
+Programmatic Highlighting
+-------------------------
+
+You can programmatically highlight specific intersections using the ``highlight`` parameter.
+This is useful for drawing attention to specific patterns without requiring user interaction.
+
+Highlighting the Largest Intersection
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Highlight the intersection with the most users:
+
+.. altair-plot::
+
+    au.UpSetAltair(
+        data=data,
+        sets=platforms,
+        title="Social Media Platform Usage - Largest Intersection Highlighted",
+        highlight="greatest",
+        width=800,
+        height=500
+    ).chart
+
+Highlighting the Smallest Intersection
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Highlight the intersection with the fewest users:
+
+.. altair-plot::
+
+    au.UpSetAltair(
+        data=data,
+        sets=platforms,
+        title="Social Media Platform Usage - Smallest Intersection Highlighted",
+        highlight="least",
+        width=800,
+        height=500
+    ).chart
+
+Highlighting Specific Intersections by Index
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Highlight specific intersections by their index (0-based):
+
+.. altair-plot::
+
+    # Highlight the first intersection
+    au.UpSetAltair(
+        data=data,
+        sets=platforms,
+        title="Social Media Platform Usage - First Intersection Highlighted",
+        highlight=0,
+        width=800,
+        height=500
+    ).chart
+
+Highlighting Multiple Intersections
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Highlight multiple intersections at once:
+
+.. altair-plot::
+
+    # Highlight the first three intersections
+    au.UpSetAltair(
+        data=data,
+        sets=platforms,
+        title="Social Media Platform Usage - Multiple Intersections Highlighted",
+        highlight=[0, 1, 2],
+        width=800,
+        height=500
+    ).chart