Sorts inversely selection (or grid if none)

        corresponding to column of key

def sort_descending(self, key):
        """Sorts inversely selection (or grid if none)

        corresponding to column of key

        """

        row, col, tab = key

        scells = self.grid.code_array[:, col, tab]
        sorted_row_idxs = sorted(xrange(len(scells)), key=scells.__getitem__)
        sorted_row_idxs.reverse()

        self.replace_cells(key, sorted_row_idxs)

        self.grid.ForceRefresh()