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BUG: drop_duplicates drops name(s). #10116

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BUG: drop_duplicates drops name(s). #10116

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1 change: 1 addition & 0 deletions .gitignore
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Expand Up @@ -41,6 +41,7 @@ doc/_build
dist
# Egg metadata
*.egg-info
.eggs
# tox testing tool
.tox
# rope
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v0.17.0.txt
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Expand Up @@ -65,6 +65,6 @@ Bug Fixes

- Bug in ``Timestamp``'s' ``microsecond``, ``quarter``, ``dayofyear``, ``week`` and ``daysinmonth`` properties return ``np.int`` type, not built-in ``int``. (:issue:`10050`)
- Bug in ``NaT`` raises ``AttributeError`` when accessing to ``daysinmonth``, ``dayofweek`` properties. (:issue:`10096`)

- Bug in ``drop_duplicates`` dropping name(s) (:issue:`10115`)


5 changes: 4 additions & 1 deletion pandas/core/index.py
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Expand Up @@ -2580,7 +2580,10 @@ def drop(self, labels, errors='raise'):
@Appender(_shared_docs['drop_duplicates'] % _index_doc_kwargs)
def drop_duplicates(self, take_last=False):
result = super(Index, self).drop_duplicates(take_last=take_last)
return self._constructor(result)
if self.name is not None:
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This check is for dealing with the API differences between Index and MultiIndex, yes? I think it would be cleaner to override the method on MultiIndex.

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Yes. OK, I can do that.

Alternatively, it would be great if the constructors of all Index subclasses (other than MultiIndex) accepted a names list of length one and used it to set name. That way one could always just set names without worrying about it.

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I would even be happy if you just explicitly check isinstance(self, MultiIndex).

I agree that your alternative solution would be preferable. That's part of a much bigger issue: #3268

return self._constructor(result, name=self.name)
else:
return self._constructor(result, names=self.names)
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you can dispense with this with a

return self._shallow_copy(result), should handle all meta-data

e.g. this will propogate things like freq/tz, etc as well.

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though looking at this now, I think MultiIndex._shallow_copy is wrong

let me see if I can fix this

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seth-p#1


@Appender(_shared_docs['duplicated'] % _index_doc_kwargs)
def duplicated(self, take_last=False):
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11 changes: 11 additions & 0 deletions pandas/tests/test_index.py
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Expand Up @@ -4151,6 +4151,17 @@ def test_droplevel_multiple(self):
expected = index[:2].droplevel(2).droplevel(0)
self.assertTrue(dropped.equals(expected))

def test_drop_duplicates_names(self):
# GH 10115
for idx in [Index([3, 4, 5, 3]),
Index([3, 4, 5, 3], name='Num'),
MultiIndex.from_tuples([('A', 1), ('A', 2)]),
MultiIndex.from_tuples([('A', 1), ('A', 2)], names=[None, None]),
MultiIndex.from_tuples([('A', 1), ('A', 2)], names=[None, 'Num']),
MultiIndex.from_tuples([('A', 1), ('A', 2)], names=['Upper', 'Num']),
]:
self.assertEqual(idx.drop_duplicates().names, idx.names)

def test_insert(self):
# key contained in all levels
new_index = self.index.insert(0, ('bar', 'two'))
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