Summary

This PR addsfacet_row support toplotly.express.imshow, enabling visualization of 4D and 5D data by faceting along both row and column dimensions.

Closes#4108

Motivation

Currently,px.imshow only supportsfacet_col for creating faceted plots, limiting users to visualizing 3D data (with one facet dimension). Many scientific and
engineering use cases require visualizing 4D tensor data (e.g., full factorial experimental designs in ML and biological sciences). This PR enables users to use both
facet_row andfacet_col simultaneously, along withanimation_frame, to visualize up to 5D datasets.

Changes

plotly/express/_imshow.py

• Addedfacet_row parameter to the function signature
• Updated docstring to document the new parameter
• Updated slice dimension calculations to handle bothfacet_row andfacet_col
• Updated xarray handling to extractfacet_row dimension labels
• Updated array reshaping to handle the additional dimension
• Updated figure building to generate row labels and place traces correctly
• Note:facet_col_wrap is ignored whenfacet_row is set (consistent with other px functions)

tests/test_optional/test_px/test_imshow.py

• Addedtest_facet_row: Tests facet_row with numpy arrays
• Addedtest_facet_row_and_col: Tests using both facet_row and facet_col together
• Addedtest_animation_facet_row_and_col: Tests animation + facet_row + facet_col
• Addedtest_imshow_xarray_facet_row: Tests facet_row with xarray
• Addedtest_imshow_xarray_facet_row_and_col: Tests both facets with xarray

Example Usage

importplotly.expressaspx# Prepare data for multi dimensional usagedf=px.data.tips()cols= ['smoker','sex','time','day','size']pivot=df.groupby(cols)['total_bill'].mean().reset_index()da=pivot.set_index(cols).to_xarray()['total_bill']# 4D data: visualize with facet_row and facet_colfig1=px.imshow(da.sum('day'),facet_row="smoker",facet_col="sex")fig1.show()# Also works with numpyfig2=px.imshow(da.sum('day').values,facet_row=0,facet_col=1)fig2.show()# 5D data: animation + facet_row + facet_colfig3=px.imshow(da,facet_row="smoker",facet_col="sex",animation_frame='day')fig3.show()