ENH: Add union_categories parameter to pd.concat#65098
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jbrockmendel wants to merge 3 commits intopandas-dev:mainfrom
Open
ENH: Add union_categories parameter to pd.concat#65098jbrockmendel wants to merge 3 commits intopandas-dev:mainfrom
jbrockmendel wants to merge 3 commits intopandas-dev:mainfrom
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Add a `union_categories` keyword to `pd.concat` that preserves categorical dtype by taking the union of categories when concatenating Categoricals with different category sets. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Use already-imported CategoricalDtype for the isinstance check and call _concat_same_type via the first element instead of importing Categorical. Also clean up docstring to refer to dtype not class. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Cast to Sequence[ExtensionArray] to satisfy mypy after the CategoricalDtype isinstance check. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Adds a
union_categorieskeyword topd.concatthat preserves categorical dtype by taking the union of categories when concatenating Categoricals with different category setscloses API: union_categoricals in concat #14177
closes BUG: pd.concat doesn't preserve categorical dtypes #51362
closes BUG: Concat does not preserve category if lists of categories do not match. #42840
closes append a categorical with different categories to the existing #12509
Test plan
Falsepreserves existing behavior🤖 Generated with Claude Code