merge master

Author: charlesdong1991

doc/source/whatsnew/v0.25.0.rst

@@ -21,6 +21,7 @@ Other Enhancements
 
 - Indexing of ``DataFrame`` and ``Series`` now accepts zerodim ``np.ndarray`` (:issue:`24919`)
 - :meth:`Timestamp.replace` now supports the ``fold`` argument to disambiguate DST transition times (:issue:`25017`)
+- :function:`pandas.merge` now accepts ``None`` as input of suffixes (:issue:`25242`)
 - :meth:`DataFrame.at_time` and :meth:`Series.at_time` now support :meth:`datetime.time` objects with timezones (:issue:`24043`)
 - ``Series.str`` has gained :meth:`Series.str.casefold` method to removes all case distinctions present in a string (:issue:`25405`)
 - :meth:`DataFrame.set_index` now works for instances of ``abc.Iterator``, provided their output is of the same length as the calling frame (:issue:`22484`, :issue:`24984`)

pandas/core/frame.py

@@ -273,14 +273,6 @@
 4  bar           2  bar            6
 5  baz           3  baz            7
 
-Merge DataFrames df1 and df2, but raise an exception if the DataFrames have
-any overlapping columns.
-
->>> df1.merge(df2, left_on='lkey', right_on='rkey', suffixes=(False, False))
-Traceback (most recent call last):
-...
-ValueError: columns overlap but no suffix specified:
-    Index(['value'], dtype='object')
 """
 
 # -----------------------------------------------------------------------

pandas/core/internals/managers.py

@@ -1963,9 +1963,6 @@ def items_overlap_with_suffix(left, lsuffix, right, rsuffix):
     if len(to_rename) == 0:
         return left, right
     else:
-        if not lsuffix and not rsuffix:
-            raise ValueError('columns overlap but no suffix specified: '
-                             '{rename}'.format(rename=to_rename))
 
         def renamer(x, suffix):
             """Rename the left and right indices.

pandas/core/reshape/merge.py

@@ -159,13 +159,13 @@ def merge_ordered(left, right, on=None,
         left DataFrame
     fill_method : {'ffill', None}, default None
         Interpolation method for data
-    suffixes : Sequence, default is ("_x", "_y")
+    suffixes : Sequence or None, default is ("_x", "_y")
         A length-2 sequence where each element is optionally a string
         indicating the suffix to add to overlapping column names in
         `left` and `right` respectively. Pass a value of `None` instead
         of a string to indicate that the column name from `left` or
-        `right` should be left as-is, with no suffix. At least one of the
-        values must not be None.
+        `right` should be left as-is, with no suffix. `None` means
+        keep both name of overlapping columns as-is.
 
         .. versionchanged:: 0.25.0
     how : {'left', 'right', 'outer', 'inner'}, default 'outer'
@@ -495,6 +495,8 @@ def __init__(self, left, right, how='inner', on=None,
 
         self.copy = copy
         self.suffixes = suffixes
+        if self.suffixes is None:
+            self.suffixes = (None, None)
         self.sort = sort
 
         self.left_index = left_index

pandas/tests/frame/test_join.py

@@ -97,12 +97,6 @@ def test_join_index(frame):
     with pytest.raises(ValueError, match='join method'):
         f.join(f2, how='foo')
 
-    # corner case - overlapping columns
-    msg = 'columns overlap but no suffix'
-    for how in ('outer', 'left', 'inner'):
-        with pytest.raises(ValueError, match=msg):
-            frame.join(frame, how=how)
-
 
 def test_join_index_more(frame):
     af = frame.loc[:, ['A', 'B']]

pandas/tests/reshape/merge/test_merge.py

@@ -1618,7 +1618,18 @@ def test_merge_series(on, left_on, right_on, left_index, right_index, nm):
     ("a", "a", dict(suffixes=[None, "_x"]), ["a", "a_x"]),
     (0, 0, dict(suffixes=["_a", None]), ["0_a", 0]),
     ("a", "a", dict(), ["a_x", "a_y"]),
-    (0, 0, dict(), ["0_x", "0_y"])
+    (0, 0, dict(), ["0_x", "0_y"]),
+    # accept 2-length None alike suffixes input
+    (0, 0, dict(suffixes=[None, None]), [0, 0]),
+    (0, 0, dict(suffixes=(None, '')), [0, '0']),
+    (0, 0, dict(suffixes=['', '']), ['0', '0']),
+    ("a", "a", dict(suffixes=[None, None]), ["a", "a"]),
+    ("a", "a", dict(suffixes=["", None]), ["a", "a"]),
+    ("a", "a", dict(suffixes=(None, None)), ["a", "a"]),
+    ("a", "a", dict(suffixes=('', '')), ["a", "a"]),
+    # accept None as suffixes
+    (0, 0, dict(suffixes=None), [0, 0]),
+    ("a", "a", dict(suffixes=None), ["a", "a"])
 ])
 def test_merge_suffix(col1, col2, kwargs, expected_cols):
     # issue: 24782
@@ -1633,36 +1644,3 @@ def test_merge_suffix(col1, col2, kwargs, expected_cols):
 
     result = pd.merge(a, b, left_index=True, right_index=True, **kwargs)
     tm.assert_frame_equal(result, expected)
-
-
-@pytest.mark.parametrize("col1, col2, suffixes", [
-    ("a", "a", [None, None]),
-    ("a", "a", (None, None)),
-    ("a", "a", ("", None)),
-    (0, 0, [None, None]),
-    (0, 0, (None, ""))
-])
-def test_merge_suffix_error(col1, col2, suffixes):
-    # issue: 24782
-    a = pd.DataFrame({col1: [1, 2, 3]})
-    b = pd.DataFrame({col2: [3, 4, 5]})
-
-    # TODO: might reconsider current raise behaviour, see issue 24782
-    msg = "columns overlap but no suffix specified"
-    with pytest.raises(ValueError, match=msg):
-        pd.merge(a, b, left_index=True, right_index=True, suffixes=suffixes)
-
-
-@pytest.mark.parametrize("col1, col2, suffixes", [
-    ("a", "a", None),
-    (0, 0, None)
-])
-def test_merge_suffix_none_error(col1, col2, suffixes):
-    # issue: 24782
-    a = pd.DataFrame({col1: [1, 2, 3]})
-    b = pd.DataFrame({col2: [3, 4, 5]})
-
-    # TODO: might reconsider current raise behaviour, see GH24782
-    msg = "iterable"
-    with pytest.raises(TypeError, match=msg):
-        pd.merge(a, b, left_index=True, right_index=True, suffixes=suffixes)

pandas/tests/reshape/merge/test_multi.py

@@ -508,12 +508,6 @@ def test_join_multi_levels(self):
         with pytest.raises(ValueError):
             household.join(portfolio, how='inner')
 
-        portfolio2 = portfolio.copy()
-        portfolio2.index.set_names(['household_id', 'foo'])
-
-        with pytest.raises(ValueError):
-            portfolio2.join(portfolio, how='inner')
-
     def test_join_multi_levels2(self):
 
         # some more advanced merges