def edge_history(self, source, target, attribute):
        """
        Returns a dictionary of attribute vales for each Graph in the
        :class:`.GraphCollection` for a single edge.

        Parameters
        ----------
        source : str
            Identifier for source node.
        target : str
            Identifier for target node.
        attribute : str
            The attribute of interest; e.g. 'betweenness_centrality'

        Returns
        -------
        history : dict
        """

        return {attr['graph']: attr[attribute] for i, attr
                in self.master_graph.edge[source][target].items()}