Extract coordinates from indexers.
        Returns an OrderedDict mapping from coordinate name to the
        coordinate variable.

        Only coordinate with a name different from any of self.variables will
        be attached.

def _get_indexers_coords_and_indexes(self, indexers):
        """  Extract coordinates from indexers.
        Returns an OrderedDict mapping from coordinate name to the
        coordinate variable.

        Only coordinate with a name different from any of self.variables will
        be attached.
        """
        from .dataarray import DataArray

        coord_list = []
        indexes = OrderedDict()
        for k, v in indexers.items():
            if isinstance(v, DataArray):
                v_coords = v.coords
                if v.dtype.kind == 'b':
                    if v.ndim != 1:  # we only support 1-d boolean array
                        raise ValueError(
                            '{:d}d-boolean array is used for indexing along '
                            'dimension {!r}, but only 1d boolean arrays are '
                            'supported.'.format(v.ndim, k))
                    # Make sure in case of boolean DataArray, its
                    # coordinate also should be indexed.
                    v_coords = v[v.values.nonzero()[0]].coords

                coord_list.append({d: v_coords[d].variable for d in v.coords})
                indexes.update(v.indexes)

        # we don't need to call align() explicitly or check indexes for
        # alignment, because merge_variables already checks for exact alignment
        # between dimension coordinates
        coords = merge_variables(coord_list)
        assert_coordinate_consistent(self, coords)

        # silently drop the conflicted variables.
        attached_coords = OrderedDict(
            (k, v) for k, v in coords.items() if k not in self._variables
        )
        attached_indexes = OrderedDict(
            (k, v) for k, v in indexes.items() if k not in self._variables
        )
        return attached_coords, attached_indexes