On 07/16/2014 05:44 PM, Flavien Lambert wrote:
On the same topic, I did not find the function for getting the edge from the edge index. There is one for vertices like vertex(n) but for edges?
There is no such function, and this is related to the speed difference you are seeing. The edges are not stored in one big vector, and thus cannot be addressed simply by its index. Instead, they are stored in different vectors across all nodes (i.e. and adjacency list), and thus one needs to iterate first through the vectors. Now lets look at your code:
_edges = [_e for _e in _network.edges()] %time for _e in _network.edges() : a = _speeds[_e]
_speedDict = {} for _e in _edges : _speedDict[_network.edge_index[_e]] = _speeds[_e] _indexes = [_network.edge_index[_e] for _e in _network.edges()] %time for _n in _indexes : a = _speedDict[_n]
What makes the second loop slower has little to do with property maps vs dicts, but instead with the loop over the Graph.edges() iterator and the loop ofter the list you created in the second part. Whenever you loop over the edges, not only is the loop slightly slower because it is not a simple list, but a "list of lists", but also (more importantly) because it has to *create* edge descriptor objects at each iteration! In the second loop you created these objects and stored them in a list, and then looped over this list, which does not involve object creation, and is therefore much faster. Best, Tiago -- Tiago de Paula Peixoto <tiago@skewed.de>