code: def stack(self, dimensions=None, **dimensions_kwargs):
          
          ds = self._to_temp_dataset().stack(dimensions, **dimensions_kwargs)
          return self._from_temp_dataset(ds)
docs: 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