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BUG: Fixed handling of non-list value_vars in melt #15351

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BUG: Fixed handling of non-list value_vars in melt #15351

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33728de
BUG: Fixed handling of non-list value_vars in melt
Feb 8, 2017
d4c5da3
Improved type checking and tests. Added whatsnew note.
jbradt Feb 9, 2017
7406222
Fixed formatting. Added comment with issue number to test.
Feb 9, 2017
455a310
Tested types when using MultiIndex to ensure they are lists.
Feb 9, 2017
70d7256
Merge branch 'master' into fix-melt
jbradt Feb 9, 2017
129d531
Moved binary operators to satisfy flake8
Feb 10, 2017
20159c1
Changed exception classes to ValueError.
Feb 10, 2017
e907135
Split test into two parts
Feb 10, 2017
3038f64
Merge remote-tracking branch 'upstream/master' into fix-melt
Feb 10, 2017
a2f2510
Changed to tm.assertRaisesRegexp for Python 2 compat.
Feb 10, 2017
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2 changes: 2 additions & 0 deletions pandas/core/reshape.py
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Original file line number Diff line number Diff line change
Expand Up @@ -771,6 +771,8 @@ def melt(frame, id_vars=None, value_vars=None, var_name=None,
if value_vars is not None:
if not isinstance(value_vars, (tuple, list, np.ndarray)):
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this checking (and in the clause above) should be not is_list_like(value_vars)

value_vars = [value_vars]
else:
value_vars = list(value_vars)
frame = frame.loc[:, id_vars + value_vars]
else:
frame = frame.copy()
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14 changes: 14 additions & 0 deletions pandas/tests/test_reshape.py
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Expand Up @@ -56,6 +56,20 @@ def test_value_vars(self):
columns=['id1', 'id2', 'variable', 'value'])
tm.assert_frame_equal(result4, expected4)

def test_value_vars_types(self):
result_with_tuple = melt(self.df, id_vars=['id1', 'id2'], value_vars=('A', 'B'))
result_with_array = melt(self.df, id_vars=['id1', 'id2'], value_vars=np.array(['A', 'B']))
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you can do the result checking in a loop, use a list as well


expected = DataFrame({'id1': self.df['id1'].tolist() * 2,
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can you add the issue number as a comment

'id2': self.df['id2'].tolist() * 2,
'variable': ['A'] * 10 + ['B'] * 10,
'value': (self.df['A'].tolist() +
self.df['B'].tolist())},
columns=['id1', 'id2', 'variable', 'value'])

tm.assert_frame_equal(result_with_tuple, expected)
tm.assert_frame_equal(result_with_array, expected)

def test_custom_var_name(self):
result5 = melt(self.df, var_name=self.var_name)
self.assertEqual(result5.columns.tolist(), ['var', 'value'])
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