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df.combine_first() with empty frame should still yield unioned index #2332

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df.combine_first() with empty frame should still yield unioned index #2332

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dcfc50b
TST: combining frame with empty frame still unions index
Nov 22, 2012
7a79b1c
BUG: combining frame with empty frame still unions index. #2307
Nov 22, 2012
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11 changes: 7 additions & 4 deletions pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3503,15 +3503,18 @@ def combine(self, other, func, fill_value=None):
-------
result : DataFrame
"""
if other.empty:
return self.copy()

if self.empty:
return other.copy()
other_idxlen = len(other.index) # save for compare

this, other = self.align(other, copy=False)
new_index = this.index

if other.empty and len(new_index) == len(self.index):
return self.copy()

if self.empty and len(other) == other_idxlen:
return other.copy()

# sorts if possible
new_columns = this.columns.union(other.columns)
do_fill = fill_value is not None
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3 changes: 3 additions & 0 deletions pandas/tests/test_frame.py
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Expand Up @@ -6131,6 +6131,9 @@ def test_combine_first(self):
comb = self.empty.combine_first(self.frame)
assert_frame_equal(comb, self.frame)

comb = self.frame.combine_first(DataFrame(index=["faz","boo"]))
self.assertTrue("faz" in comb.index)

def test_combine_first_mixed_bug(self):
idx = Index(['a','b','c','e'])
ser1 = Series([5.0,-9.0,4.0,100.],index=idx)
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