Creates a clone of the Layout with the nth-frame for each
        Element.

def _get_frame(self, key):
        """
        Creates a clone of the Layout with the nth-frame for each
        Element.
        """
        cached = self.current_key is None
        layout_frame = self.layout.clone(shared_data=False)
        if key == self.current_key and not self._force:
            return self.current_frame
        else:
            self.current_key = key

        key_map = dict(zip([d.name for d in self.dimensions], key))
        for path, item in self.layout.items():
            frame = get_nested_plot_frame(item, key_map, cached)
            if frame is not None:
                layout_frame[path] = frame
        traverse_setter(self, '_force', False)

        self.current_frame = layout_frame
        return layout_frame