s.str.split : Split string values on specified separator.
        Series.unstack : Unstack, a.k.a. pivot, Series with MultiIndex
            to produce DataFrame.
        DataFrame.melt : Unpivot a DataFrame from wide format to long format.
        DataFrame.explode : Explode a DataFrame from list-like
            columns to long format.

        Notes
        -----
        This routine will explode list-likes including lists, tuples, sets,
        Series, and np.ndarray. The result dtype of the subset rows will
        be object. Scalars will be returned unchanged, and empty list-likes will
        result in a np.nan for that row. In addition, the ordering of elements in
        the output will be non-deterministic when exploding sets.

        Reference :ref:`the user guide <reshaping.explode>` for more examples.

        Examples
        --------
        >>> s = pd.Series([[1, 2, 3], 'foo', [], [3, 4]])
        >>> s
        0    [1, 2, 3]
        1          foo
        2           []
        3       [3, 4]
        dtype: object

        >>> s.explode()
        0      1
        0      2
        0      3
        1    foo
        2    NaN
        3      3
        3      4
        dtype: object
        T)