Make DataFrame.pivot index argument truly optional #3962
Description
Creating a pivot table from a DataFrame is easy.
In [17]: df Out[17]: date variable value 0 2000-01-03 00:00:00 A 0.528219 1 2000-01-04 00:00:00 A -0.135071 2 2000-01-05 00:00:00 A -0.343018 3 2000-01-03 00:00:00 B -0.097701 4 2000-01-04 00:00:00 B -1.383248 In [18]: df.pivot('date', 'variable', 'value') Out[18]: variable A B date 2000-01-03 0.528219 -0.097701 2000-01-04 -0.135071 -1.383248 2000-01-05 -0.343018 NaNHowever if the index has been set, and there is no column to be set as index, pivot fails. From api point of view, the index argument is optional, but in fact it is not.
In [19]: df.set_index('date', inplace=True) In [20]: df Out[20]: variable value date 2000-01-03 A 0.528219 2000-01-04 A -0.135071 2000-01-05 A -0.343018 2000-01-03 B -0.097701 2000-01-04 B -1.383248 In [21]: df.pivot(columns='variable', values='value') --------------------------------------------------------------------------- KeyError Traceback (most recent call last) ... KeyError: u'no item named None'Of course one can reset the index before using pivot.
In [22]: df.reset_index().pivot('date', 'variable', 'value') Out[22]: variable A B date 2000-01-03 0.528219 -0.097701 2000-01-04 -0.135071 -1.383248 2000-01-05 -0.343018 NaN