code: def edge_statistics(docgraph):
      
      print "Edge statistics\n==============="
      layer_counts = Counter()
      attrib_counts = Counter()
      source_counts = Counter()
      target_counts = Counter()
      for source, target, edge_attrs in docgraph.edges_iter(data=True):
          for layer in edge_attrs['layers']:
              layer_counts[layer] += 1
          for attrib in edge_attrs:
              attrib_counts[attrib] += 1
          source_counts[source] += 1
          target_counts[target] += 1
  
      print "\nnumber of edges with layers"
      print_sorted_counter(layer_counts)
      print "\nnumber of edges with attributes"
      print_sorted_counter(attrib_counts)
  
      print "\nmost common source edges"
      print_most_common(source_counts)
      print "\nmost common target edges"
      print_most_common(target_counts)
docs: print basic statistics about an edge, e.g. layer/attribute counts