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BUG: concat on axis=0 with categorical (GH10177) #10179

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Jun 27, 2015
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BUG: concat on axis=0 with categorical (GH10177) #10179

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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v0.17.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -103,4 +103,4 @@ Bug Fixes
- Bug that caused segfault when resampling an empty Series (:issue:`10228`)
- Bug in ``DatetimeIndex`` and ``PeriodIndex.value_counts`` resets name from its result, but retains in result's ``Index``. (:issue:`10150`)


- Bug in `pandas.concat` with ``axis=0`` when column is of dtype ``category`` (:issue:`10177`)
2 changes: 1 addition & 1 deletion pandas/core/internals.py
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Expand Up @@ -4133,7 +4133,7 @@ def get_empty_dtype_and_na(join_units):
else:
return np.dtype(np.bool_), None
elif 'category' in upcast_classes:
return com.CategoricalDtype(), np.nan
return np.dtype(np.object_), np.nan
elif 'float' in upcast_classes:
return np.dtype(np.float64), np.nan
elif 'datetime' in upcast_classes:
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18 changes: 18 additions & 0 deletions pandas/tests/test_categorical.py
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Expand Up @@ -2967,6 +2967,24 @@ def test_pickle_v0_15_2(self):
#
self.assert_categorical_equal(cat, pd.read_pickle(pickle_path))

def test_concat_categorical(self):
# See GH 10177
df1 = pd.DataFrame(np.arange(18).reshape(6, 3), columns=["a", "b", "c"])
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add the issue number as a comment here


df2 = pd.DataFrame(np.arange(14).reshape(7, 2), columns=["a", "c"])
df2['h'] = pd.Series(pd.Categorical(["one", "one", "two", "one", "two", "two", "one"]))

df_concat = pd.concat((df1, df2), axis=0).reset_index(drop=True)

df_expected = pd.DataFrame({'a': [0, 3, 6, 9, 12, 15, 0, 2, 4, 6, 8, 10, 12],
'b': [1, 4, 7, 10, 13, 16, np.nan, np.nan, np.nan, np.nan, np.nan, np.nan, np.nan],
'c': [2, 5, 8, 11, 14, 17, 1, 3, 5, 7, 9, 11, 13]})
df_expected['h'] = pd.Series(pd.Categorical([None, None, None, None, None, None,
"one", "one", "two", "one", "two", "two", "one"]))

tm.assert_frame_equal(df_expected, df_concat)



if __name__ == '__main__':
import nose
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