Stack any number of existing dimensions into a single new dimension.

        New dimensions will be added at the end, and the corresponding
        coordinate variables will be combined into a MultiIndex.

        Parameters
        ----------
        dimensions : Mapping of the form new_name=(dim1, dim2, ...)
            Names of new dimensions, and the existing dimensions that they
            replace.
        **dimensions_kwargs:
            The keyword arguments form of ``dimensions``.
            One of dimensions or dimensions_kwargs must be provided.

        Returns
        -------
        stacked : DataArray
            DataArray with stacked data.

        Examples
        --------

        >>> arr = DataArray(np.arange(6).reshape(2, 3),
        ...                 coords=[('x', ['a', 'b']), ('y', [0, 1, 2])])
        >>> arr
        <xarray.DataArray (x: 2, y: 3)>
        array([[0, 1, 2],
               [3, 4, 5]])
        Coordinates:
          * x        (x) |S1 'a' 'b'
          * y        (y) int64 0 1 2
        >>> stacked = arr.stack(z=('x', 'y'))
        >>> stacked.indexes['z']
        MultiIndex(levels=[['a', 'b'], [0, 1, 2]],
                   labels=[[0, 0, 0, 1, 1, 1], [0, 1, 2, 0, 1, 2]],
                   names=['x', 'y'])

        See also
        --------
        DataArray.unstack

def stack(self, dimensions=None, **dimensions_kwargs):
        """
        Stack any number of existing dimensions into a single new dimension.

        New dimensions will be added at the end, and the corresponding
        coordinate variables will be combined into a MultiIndex.

        Parameters
        ----------
        dimensions : Mapping of the form new_name=(dim1, dim2, ...)
            Names of new dimensions, and the existing dimensions that they
            replace.
        **dimensions_kwargs:
            The keyword arguments form of ``dimensions``.
            One of dimensions or dimensions_kwargs must be provided.

        Returns
        -------
        stacked : DataArray
            DataArray with stacked data.

        Examples
        --------

        >>> arr = DataArray(np.arange(6).reshape(2, 3),
        ...                 coords=[('x', ['a', 'b']), ('y', [0, 1, 2])])
        >>> arr
        <xarray.DataArray (x: 2, y: 3)>
        array([[0, 1, 2],
               [3, 4, 5]])
        Coordinates:
          * x        (x) |S1 'a' 'b'
          * y        (y) int64 0 1 2
        >>> stacked = arr.stack(z=('x', 'y'))
        >>> stacked.indexes['z']
        MultiIndex(levels=[['a', 'b'], [0, 1, 2]],
                   labels=[[0, 0, 0, 1, 1, 1], [0, 1, 2, 0, 1, 2]],
                   names=['x', 'y'])

        See also
        --------
        DataArray.unstack
        """
        ds = self._to_temp_dataset().stack(dimensions, **dimensions_kwargs)
        return self._from_temp_dataset(ds)