ENH: Make index optional in pivot. Closes #3962

TST: Test for index is None in pivot DOC: Add release note DOC: Formatting DOC: Document index=None

Author: jseabold

doc/source/whatsnew/v0.17.0.txt

@@ -110,6 +110,8 @@ Other enhancements
 
 - ``pd.merge`` will now allow duplicate column names if they are not merged upon (:issue:`10639`).
 
+- ``pd.pivot`` will now allow passing index as ``None`` (:issue:`3962`).
+
 .. _whatsnew_0170.api:
 
 .. _whatsnew_0170.api_breaking:

pandas/core/frame.py

@@ -3460,8 +3460,9 @@ def pivot(self, index=None, columns=None, values=None):
 
  Parameters
  ----------
- index : string or object
- Column name to use to make new frame's index
+ index : string or object, optional
+ Column name to use to make new frame's index. If None, uses
+ existing index.
  columns : string or object
  Column name to use to make new frame's columns
  values : string or object, optional

pandas/core/reshape.py

@@ -319,11 +319,17 @@ def pivot(self, index=None, columns=None, values=None):
  See DataFrame.pivot
  """
  if values is None:
- indexed = self.set_index([index, columns])
+ cols = [columns] if index is None else [index, columns]
+ append = index is None
+ indexed = self.set_index(cols, append=append)
  return indexed.unstack(columns)
  else:
+ if index is None:
+ index = self.index
+ else:
+ index = self[index]
  indexed = Series(self[values].values,
- index=MultiIndex.from_arrays([self[index],
+ index=MultiIndex.from_arrays([index,
  self[columns]]))
  return indexed.unstack(columns)
 

pandas/tests/test_frame.py

@@ -9478,6 +9478,47 @@ def test_pivot_integer_bug(self):
  repr(result)
  self.assert_numpy_array_equal(result.columns, ['A', 'B'])
 
+ def test_pivot_index_none(self):
+ # gh-3962
+ data = {
+ 'index': ['A', 'B', 'C', 'C', 'B', 'A'],
+ 'columns': ['One', 'One', 'One', 'Two', 'Two', 'Two'],
+ 'values': [1., 2., 3., 3., 2., 1.]
+ }
+
+ frame = DataFrame(data).set_index('index')
+ result = frame.pivot(columns='columns', values='values')
+ expected = DataFrame({
+ 'One': {'A': 1., 'B': 2., 'C': 3.},
+ 'Two': {'A': 1., 'B': 2., 'C': 3.}
+ })
+
+ expected.index.name, expected.columns.name = 'index', 'columns'
+ assert_frame_equal(result, expected)
+
+ # omit values
+ result = frame.pivot(columns='columns')
+
+ expected.columns = pd.MultiIndex.from_tuples([('values', 'One'),
+ ('values', 'Two')],
+ names=[None, 'columns'])
+ expected.index.name = 'index'
+ assert_frame_equal(result, expected, check_names=False)
+ self.assertEqual(result.index.name, 'index',)
+ self.assertEqual(result.columns.names, (None, 'columns'))
+ expected.columns = expected.columns.droplevel(0)
+
+ data = {
+ 'index': range(7),
+ 'columns': ['One', 'One', 'One', 'Two', 'Two', 'Two'],
+ 'values': [1., 2., 3., 3., 2., 1.]
+ }
+
+ result = frame.pivot(columns='columns', values='values')
+
+ expected.columns.name = 'columns'
+ assert_frame_equal(result, expected)
+
  def test_reindex(self):
  newFrame = self.frame.reindex(self.ts1.index)