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BUG: Spurious matches in DataFrame.duplicated when keep=False #11894

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BUG: Spurious matches in DataFrame.duplicated when keep=False #11894

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2 changes: 2 additions & 0 deletions doc/source/whatsnew/v0.18.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -468,9 +468,11 @@ Bug Fixes
- Bug in ``to_numeric`` where it does not raise if input is more than one dimension (:issue:`11776`)

- Bug in parsing timezone offset strings with non-zero minutes (:issue:`11708`)

- Bug in ``df.plot`` using incorrect colors for bar plots under matplotlib 1.5+ (:issue:`11614`)
- Bug in the ``groupby`` ``plot`` method when using keyword arguments (:issue:`11805`).

- Bug in ``DataFrame.duplicated`` and ``drop_duplicates`` causing spurious matches when setting `keep=False` (:issue:`11864`)

- Bug in ``.loc`` result with duplicated key may have ``Index`` with incorrect dtype (:issue:`11497`)
- Bug in ``pd.rolling_median`` where memory allocation failed even with sufficient memory (:issue:`11696`)
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3 changes: 2 additions & 1 deletion pandas/hashtable.pyx
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Expand Up @@ -1067,7 +1067,8 @@ def mode_int64(int64_t[:] values):
@cython.boundscheck(False)
def duplicated_int64(ndarray[int64_t, ndim=1] values, object keep='first'):
cdef:
int ret = 0, value, k
int ret = 0, k
int64_t value
Py_ssize_t i, n = len(values)
kh_int64_t * table = kh_init_int64()
ndarray[uint8_t, ndim=1, cast=True] out = np.empty(n, dtype='bool')
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7 changes: 7 additions & 0 deletions pandas/tests/test_frame.py
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Expand Up @@ -8532,6 +8532,13 @@ def test_drop_duplicates(self):
df = pd.DataFrame([[-x, x], [x, x + 4]])
assert_frame_equal(df.drop_duplicates(), df)

# GH 11864
df = pd.DataFrame([i] * 9 for i in range(16))
df = df.append([[1] + [0] * 8], ignore_index=True)
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can u run thru all of the keep options in a loop here


for keep in ['first', 'last', False]:
assert_equal(df.duplicated(keep=keep).sum(), 0)

def test_drop_duplicates_for_take_all(self):
df = DataFrame({'AAA': ['foo', 'bar', 'baz', 'bar',
'foo', 'bar', 'qux', 'foo'],
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