Add custom_data argument to px.histogram

Every other Plotly Express function that builds a trace from rows of
the data frame accepts custom_data, but histogram() never did. The
core already handles the argument generically (it is how hover_data
columns reach customdata for the other functions), so adding the
parameter is enough: the selected columns are stored per input row in
the trace's customdata and are available in the events the figure
emits, which is what Dash callbacks and selection handlers need.

Closes #3859

Author: bhaskargurram-ai

CHANGELOG.md

@@ -4,6 +4,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Added
+- Add the `custom_data` argument to `px.histogram`, so extra columns can be attached to histogram traces for use in Dash callbacks and selection events, as in the other Plotly Express functions [[#3859](https://github.com/plotly/plotly.py/issues/3859)]
+
 ### Fixed
 - Fix `mpl_to_plotly` tick marker mirroring, axis positioning, and trace visibility for twinned and overlaid subplots (such as `twinx` and `twiny`) [[#5310](https://github.com/plotly/plotly.py/pull/5310)], with thanks to @robertoffmoura for the contribution!
 - Fix `mpl_to_plotly` losing matplotlib axis line colors by exporting the color of each axis's displayed spine to the plotly x and y axis `linecolor` [[#5311](https://github.com/plotly/plotly.py/pull/5311)], with thanks to @robertoffmoura for the contribution!

plotly/express/_chart_types.py

@@ -462,6 +462,7 @@ def histogram(
     facet_col_spacing=None,
     hover_name=None,
     hover_data=None,
+    custom_data=None,
     animation_frame=None,
     animation_group=None,
     category_orders=None,

tests/test_optional/test_px/test_px.py

@@ -68,6 +68,28 @@ def test_custom_data_scatter(backend):
     )
 
 
+def test_custom_data_histogram(backend):
+    tips = nw.from_native(px.data.tips(return_type=backend))
+    # No custom data
+    fig = px.histogram(tips.to_native(), x="total_bill")
+    assert fig.data[0].customdata is None
+    # Custom data is carried per row of the input, not per bin
+    fig = px.histogram(tips.to_native(), x="total_bill", custom_data=["tip", "day"])
+    assert fig.data[0].customdata.shape == (len(tips), 2)
+    assert np.all(fig.data[0].customdata[:, 0] == tips.get_column("tip").to_numpy())
+    assert np.all(fig.data[0].customdata[:, 1] == tips.get_column("day").to_numpy())
+    # Bins are aggregates, so custom data does not show up in the hover label
+    assert fig.data[0].hovertemplate == "total_bill=%{x}<br>count=%{y}<extra></extra>"
+    # Each colored trace carries the custom data of its own rows
+    fig = px.histogram(
+        tips.to_native(), x="total_bill", color="sex", custom_data=["tip"]
+    )
+    for trace in fig.data:
+        group = tips.filter(nw.col("sex") == trace.name)
+        assert trace.customdata.shape == (len(group), 1)
+        assert np.all(trace.customdata[:, 0] == group.get_column("tip").to_numpy())
+
+
 def test_labels(backend):
     tips = nw.from_native(px.data.tips(return_type=backend))
     fig = px.scatter(