One Fill Value Is Not Enough: Preserving Columnar Types When Reindexing DataFrames

When working with DataFrames, reindexing is common. When a DataFrame is reindexed, an old index (and its associated values) is conformed to a new index, potentially reordering, contracting, or expanding the rows or columns. When a reindex expands a DataFrame, new values are needed to fill the newly created rows or columns: these are “fill values.”

When reindexing with Pandas, only a single value, via the fill_value parameter, is permitted. If that fill_value is a type incompatible with the type …

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