fix: pandas dataframe named index cells showing empty (#7942) #7944
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## Summary
Fixes an issue where pandas DataFrame index columns display empty cells in the marimo UI when using pandas 3.0+.
## Problem
In pandas 3.0, when setting a sequential integer column as an index (e.g., `df.set_index('Year')`), pandas optimizes it to a `RangeIndex` with a custom name instead of creating an `Int64Index` (pandas 2.x behavior).
The existing code in `pandas_table.py` excluded ALL `RangeIndex` instances from being reset to columns, including those with custom names. This caused the index values to be missing from the JSON output sent to the frontend, resulting in empty cells.
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botterYosuke
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Jan 23, 2026
…) (marimo-team#7944) Fixes an issue where pandas DataFrame index columns display empty cells in the marimo UI when using pandas 3.0+. Fixes marimo-team#7942 ### Problem In pandas 3.0, when setting a sequential integer column as an index (e.g., `df.set_index('Year')`), pandas optimizes it to a `RangeIndex` with a custom name instead of creating an `Int64Index` (pandas 2.x behavior). The existing code in `pandas_table.py` excluded ALL `RangeIndex` instances from being reset to columns, including those with custom names. This caused the index values to be missing from the JSON output sent to the frontend, resulting in empty cells. ### Solution Modified the condition in `to_json_str()` to only skip unnamed `RangeIndex` instances (the default 0,1,2,... index). Named `RangeIndex` instances are now properly reset to columns and included in the JSON output.
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Fixes an issue where pandas DataFrame index columns display empty cells in the marimo UI when using pandas 3.0+.
Fixes #7942
Problem
In pandas 3.0, when setting a sequential integer column as an index (e.g.,
df.set_index('Year')), pandas optimizes it to aRangeIndexwith a custom name instead of creating anInt64Index(pandas 2.x behavior).The existing code in
pandas_table.pyexcluded ALLRangeIndexinstances from being reset to columns, including those with custom names. This caused the index values to be missing from the JSON output sent to the frontend, resulting in empty cells.Solution
Modified the condition in
to_json_str()to only skip unnamedRangeIndexinstances (the default 0,1,2,... index). NamedRangeIndexinstances are now properly reset to columns and included in the JSON output.