[graph-tool] Extracting vertex subgraphs (based on property map)?

Hi, Could you suggest what is the most efficient way for: 1) extracting vertex clusters based on values in vertex property map? - e.g., for iterating through all connected components in a graph, based on result of label_components 2) saving extracted subgraphs to a file? Code that I am using is in [1] but for a large graph (~1M edges, 12k clusters) it is taking days. Is there a more optimal way? Can the function topology.mark_subgraph be of help here? - the name seems relevant but I do not know how it is used. [1] https://gist.github.com/4627494 - function save_all_graphs is called to save all the subgraphs Many thanks, Uldis