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BUG: .unique() on MultiIndex: preserve names #20571

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Merged
merged 1 commit into from
Apr 1, 2018
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BUG: .unique() on MultiIndex: preserve names #20571

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2 changes: 2 additions & 0 deletions doc/source/whatsnew/v0.23.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -1069,6 +1069,8 @@ MultiIndex
- Bug in :func:`MultiIndex.__contains__` where non-tuple keys would return ``True`` even if they had been dropped (:issue:`19027`)
- Bug in :func:`MultiIndex.set_labels` which would cause casting (and potentially clipping) of the new labels if the ``level`` argument is not 0 or a list like [0, 1, ... ] (:issue:`19057`)
- Bug in :func:`MultiIndex.get_level_values` which would return an invalid index on level of ints with missing values (:issue:`17924`)
- Bug in :func:`MultiIndex.unique` when called on empty :class:`MultiIndex` (:issue:`20568`)
- Bug in :func:`MultiIndex.unique` which would not preserve level names (:issue:`20570`)
- Bug in :func:`MultiIndex.remove_unused_levels` which would fill nan values (:issue:`18417`)
- Bug in :func:`MultiIndex.from_tuples` which would fail to take zipped tuples in python3 (:issue:`18434`)
- Bug in :func:`MultiIndex.get_loc` which would fail to automatically cast values between float and int (:issue:`18818`, :issue:`15994`)
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5 changes: 2 additions & 3 deletions pandas/core/indexes/multi.py
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Expand Up @@ -553,11 +553,10 @@ def __contains__(self, key):
@Appender(_index_shared_docs['_shallow_copy'])
def _shallow_copy(self, values=None, **kwargs):
if values is not None:
if 'name' in kwargs:
kwargs['names'] = kwargs.pop('name', None)
names = kwargs.pop('names', kwargs.pop('name', self.names))
# discards freq
kwargs.pop('freq', None)
return MultiIndex.from_tuples(values, **kwargs)
return MultiIndex.from_tuples(values, names=names, **kwargs)
return self.view()

@cache_readonly
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29 changes: 22 additions & 7 deletions pandas/tests/indexes/test_multi.py
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Expand Up @@ -2452,23 +2452,33 @@ def test_get_unique_index(self):
assert result.unique
tm.assert_index_equal(result, expected)

def test_unique(self):
mi = pd.MultiIndex.from_arrays([[1, 2, 1, 2], [1, 1, 1, 2]])
@pytest.mark.parametrize('names', [None, ['first', 'second']])
def test_unique(self, names):
mi = pd.MultiIndex.from_arrays([[1, 2, 1, 2], [1, 1, 1, 2]],
names=names)

res = mi.unique()
exp = pd.MultiIndex.from_arrays([[1, 2, 2], [1, 1, 2]])
exp = pd.MultiIndex.from_arrays([[1, 2, 2], [1, 1, 2]], names=mi.names)
tm.assert_index_equal(res, exp)

mi = pd.MultiIndex.from_arrays([list('aaaa'), list('abab')])
mi = pd.MultiIndex.from_arrays([list('aaaa'), list('abab')],
names=names)
res = mi.unique()
exp = pd.MultiIndex.from_arrays([list('aa'), list('ab')])
exp = pd.MultiIndex.from_arrays([list('aa'), list('ab')],
names=mi.names)
tm.assert_index_equal(res, exp)

mi = pd.MultiIndex.from_arrays([list('aaaa'), list('aaaa')])
mi = pd.MultiIndex.from_arrays([list('aaaa'), list('aaaa')],
names=names)
res = mi.unique()
exp = pd.MultiIndex.from_arrays([['a'], ['a']])
exp = pd.MultiIndex.from_arrays([['a'], ['a']], names=mi.names)
tm.assert_index_equal(res, exp)

# GH #20568 - empty MI
mi = pd.MultiIndex.from_arrays([[], []], names=names)
res = mi.unique()
tm.assert_index_equal(mi, res)

@pytest.mark.parametrize('level', [0, 'first', 1, 'second'])
def test_unique_level(self, level):
# GH #17896 - with level= argument
Expand All @@ -2483,6 +2493,11 @@ def test_unique_level(self, level):
expected = mi.get_level_values(level)
tm.assert_index_equal(result, expected)

# With empty MI
mi = pd.MultiIndex.from_arrays([[], []], names=['first', 'second'])
result = mi.unique(level=level)
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does this also solve the case where no level is specified?

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No, the previous test does.

expected = mi.get_level_values(level)

def test_unique_datetimelike(self):
idx1 = pd.DatetimeIndex(['2015-01-01', '2015-01-01', '2015-01-01',
'2015-01-01', 'NaT', 'NaT'])
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