title: R graph degree.distribution not working
body: <p>I cannot figure out why <code>degree.distribution</code> is not working for me. I have tried on R i386 3.0.0 and R x64 3.0.0. Here is the simple script to generate a graph and show its distribution:</p>
  
  <pre><code>library(igraph)
  
  testG = graph.empty(n=10, directed=TRUE)
  for(row in 1 : 5) {
      src = row
      dest = row + 1
      testG = add.edges(testG, rbind(src, as.numeric(dest)))
      if(row %% 2 == 0) {
          dest = row + 2
          testG = add.edges(testG, rbind(src, as.numeric(dest)))
      }
  }
  testG
  
  testD = degree.distribution(testG, v=V(testG), cumulative=FALSE)
  testD
  plot(1 : length(testD), testD, "h", main="Website Graph Degree Distribution", xlab="Degree", ylab="Probability of Degree")
  degree(testG)
  </code></pre>
  
  <p>testG shows: <code>IGRAPH D--- 10 7 --</code> (makes sense).
  testD shows: <code>NULL</code> (why?).
  The plot is with just one value at (1,1). But the graph contains nodes with other degrees, as evidenced by the output of degree(testG), which is <code>[1,3,2,4,2,2,0,0,0,0]</code>.</p>