title: Computing the un-weighted length of a weighted shortest path
body: <p>I have started investigating whether <code>igraph</code> would be a more efficient method for calculating the length of a least cost path. Using the package <code>gdistance</code> it is straightforward to supply a cost surface and generated least cost paths between two (or many) points. The function <code>costDistance</code> returns the actual length of the paths as the sum of all the segments lengths (i.e. not the cumulative COST of the least cost path).</p>
  
  <p>My question is whether there is way to do this in <code>igraph</code> so that i can compare computation time. Using <code>get.shortest.paths</code>, i can obtain the length of the shortest path between vertices, but, when edge weights  are provided, the path path length is reported as the weighted path length.</p>
  
  <p>In short: i would like to find shortest paths on a weighted network but have the lengths reported in terms of edge length, not weighted edge length.</p>
  
  <p>Note: I can see how this is possible by looping through each shortest path and then writing some extra code to just add up the unweighted edge lengths, but i fear this will cancel out my original need for increased efficiency of pairwise distance calculations over massive networks.  </p>