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DOC: clarify MultiIndex.swaplevel default behavior #62772

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DOC: clarify MultiIndex.swaplevel default behavior #62772

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d1b10ea
DOC: clarify MultiIndex.swaplevel default behavior
Oct 21, 2025
38c0991
DOC: clarify MultiIndex.swaplevel negative index
Oct 22, 2025
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42 changes: 29 additions & 13 deletions pandas/core/indexes/multi.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2607,14 +2607,18 @@ def swaplevel(self, i=-2, j=-1) -> MultiIndex:

Calling this method does not change the ordering of the values.

Default is to swap the last two levels of the MultiIndex.
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In the Parameters section can you describe what negative numbers mean?

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Details for how negative numbers behave has been added.


Parameters
----------
i : int, str, default -2
First level of index to be swapped. Can pass level name as string.
Type of parameters can be mixed.
Type of parameters can be mixed. If i is a negative int, the first
level is indexed relative to the end of the MultiIndex.
j : int, str, default -1
Second level of index to be swapped. Can pass level name as string.
Type of parameters can be mixed.
Type of parameters can be mixed. If j is a negative int, the second
level is indexed relative to the end of the MultiIndex.

Returns
-------
Expand All @@ -2626,24 +2630,36 @@ def swaplevel(self, i=-2, j=-1) -> MultiIndex:
Series.swaplevel : Swap levels i and j in a MultiIndex.
DataFrame.swaplevel : Swap levels i and j in a MultiIndex on a
particular axis.

Examples
--------
>>> mi = pd.MultiIndex(
... levels=[["a", "b"], ["bb", "aa"]], codes=[[0, 0, 1, 1], [0, 1, 0, 1]]
... levels=[["a", "b"], ["bb", "aa"], ["aaa", "bbb"]],
... codes=[[0, 0, 1, 1], [0, 1, 0, 1], [1, 0, 1, 0]],
... )
>>> mi
MultiIndex([('a', 'bb'),
('a', 'aa'),
('b', 'bb'),
('b', 'aa')],
MultiIndex([('a', 'bb', 'bbb'),
('a', 'aa', 'aaa'),
('b', 'bb', 'bbb'),
('b', 'aa', 'aaa')],
)
>>> mi.swaplevel(0, 1)
MultiIndex([('bb', 'a'),
('aa', 'a'),
('bb', 'b'),
('aa', 'b')],
>>> mi.swaplevel()
MultiIndex([('a', 'bbb', 'bb'),
('a', 'aaa', 'aa'),
('b', 'bbb', 'bb'),
('b', 'aaa', 'aa')],
)
>>> mi.swaplevel(0)
MultiIndex([('bbb', 'bb', 'a'),
('aaa', 'aa', 'a'),
('bbb', 'bb', 'b'),
('aaa', 'aa', 'b')],
)
>>> mi.swaplevel(0, 1)
MultiIndex([('bb', 'a', 'bbb'),
('aa', 'a', 'aaa'),
('bb', 'b', 'bbb'),
('aa', 'b', 'aaa')],
)
"""
new_levels = list(self.levels)
new_codes = list(self.codes)
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