Frame({'A': [1, 1, 2, 2],
        ...                    'B': [1, 2, 3, 4],
        ...                    'C': [0.362, 0.227, 1.267, -0.562]})
        >>> df
              A  B      C
        0     1  1  0.362
        1     1  2  0.227
        2     2  3  1.267
        3     2  4 -0.562

        >>> df.groupby('A').rolling(2).sum()
            B      C
        A
        1 0  NaN    NaN
          1  3.0  0.589
        2 2  NaN    NaN
          3  7.0  0.705

        >>> df.groupby('A').rolling(2, min_periods=1).sum()
            B      C
        A
        1 0  1.0  0.362
          1  3.0  0.589
        2 2  3.0  1.267
          3  7.0  0.705

        >>> df.groupby('A').rolling(2, on='B').sum()
            B      C
        A
        1 0  1    NaN
          1  2  0.589
        2 2  3    NaN
          3  4  0.705
        r