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Merged
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Sep 23, 2022
Merged

PERF: MultiIndex.size #48723

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8395c77
add MultiIndex.size
lukemanley Sep 22, 2022
2551a6f
whatsnew
lukemanley Sep 23, 2022
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.6.0.rst
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Expand Up @@ -133,6 +133,7 @@ Performance improvements
~~~~~~~~~~~~~~~~~~~~~~~~
- Performance improvement in :meth:`.DataFrameGroupBy.median` and :meth:`.SeriesGroupBy.median` and :meth:`.GroupBy.cumprod` for nullable dtypes (:issue:`37493`)
- Performance improvement in :meth:`MultiIndex.argsort` and :meth:`MultiIndex.sort_values` (:issue:`48406`)
- Performance improvement in :meth:`MultiIndex.size` (:issue:`48723`)
- Performance improvement in :meth:`MultiIndex.union` without missing values and without duplicates (:issue:`48505`)
- Performance improvement in :meth:`.DataFrameGroupBy.mean`, :meth:`.SeriesGroupBy.mean`, :meth:`.DataFrameGroupBy.var`, and :meth:`.SeriesGroupBy.var` for extension array dtypes (:issue:`37493`)
- Performance improvement in :meth:`MultiIndex.isin` when ``level=None`` (:issue:`48622`)
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8 changes: 8 additions & 0 deletions pandas/core/indexes/multi.py
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Expand Up @@ -786,6 +786,14 @@ def dtypes(self) -> Series:
def __len__(self) -> int:
return len(self.codes[0])

@property
def size(self) -> int:
"""
Return the number of elements in the underlying data.
"""
# override Index.size to avoid materializing _values
return len(self)

# --------------------------------------------------------------------
# Levels Methods

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