Initial commit

GH21220

pandas/core/reshape/merge.py

@@ -11,7 +11,7 @@
 import pandas.compat as compat
 
 from pandas import (Categorical, DataFrame,
- Index, MultiIndex, Timedelta)
+ Index, MultiIndex, Timedelta, Series)
 from pandas.core.arrays.categorical import _recode_for_categories
 from pandas.core.frame import _merge_doc
 from pandas.core.dtypes.common import (
@@ -492,6 +492,10 @@ def __init__(self, left, right, how='inner', on=None,
  left_index=False, right_index=False, sort=True,
  suffixes=('_x', '_y'), copy=True, indicator=False,
  validate=None):
+ if isinstance(left, Series):
+ left = left.to_frame()
+ if isinstance(right, Series):
+ right = right.to_frame()
  self.left = self.orig_left = left
  self.right = self.orig_right = right
  self.how = how
@@ -535,12 +539,14 @@ def __init__(self, left, right, how='inner', on=None,
  '{right_index}'.format(right_index=type(right_index)))
 
  # warn user when merging between different levels
- if left.columns.nlevels != right.columns.nlevels:
- msg = ('merging between different levels can give an unintended '
- 'result ({left} levels on the left, {right} on the right)'
- ).format(left=left.columns.nlevels,
- right=right.columns.nlevels)
- warnings.warn(msg, UserWarning)
+ if isinstance(left, DataFrame) and isinstance(right, DataFrame):
+ if left.columns.nlevels != right.columns.nlevels:
+ msg = ('merging between different levels can give an '
+ 'unintended result ({left} levels on the left, '
+ '{right} on the right)'
+ ).format(left=left.columns.nlevels,
+ right=right.columns.nlevels)
+ warnings.warn(msg, UserWarning)
 
  self._validate_specification()
 

pandas/tests/reshape/merge/test_merge.py

@@ -1864,3 +1864,24 @@ def test_merge_index_types(index):
  OrderedDict([('left_data', [1, 2]), ('right_data', [1.0, 2.0])]),
  index=index)
  assert_frame_equal(result, expected)
+
+
+def test_merge_series():
+ # GH 21220
+ a = pd.DataFrame({"A": [1, 2, 3, 4]},
+ index=pd.MultiIndex.from_product([['a', 'b'], [0, 1]],
+ names=['outer', 'inner']))
+ b = pd.Series([1, 2, 3, 4],
+ index=pd.MultiIndex.from_product([['a', 'b'], [1, 2]],
+ names=['outer', 'inner']), name='B')
+ expected = pd.DataFrame({"A": [2, 4], "B": [1, 3]},
+ index=pd.MultiIndex.from_product([['a', 'b'], [1]],
+ names=['outer', 'inner']))
+
+ # Testing current merge behvaior is as before
+ result = pd.merge(a, b.to_frame(), on=['outer', 'inner'])
+ tm.assert_frame_equal(result, expected)
+
+ # Testing changed merge behvaior is as expected
+ result = pd.merge(a, b, on=['outer', 'inner'])
+ tm.assert_frame_equal(result, expected)