[igraph] Issues trying to get tree using layout.reingold.tilford

[Andrew Marritt]

I originally posted this on stackoverflow  
(http://stackoverflow.com/questions/13867120/getting-x-y-coordinates-for-tree-graph-using-r-igraph)
 and was referred here.

I'm trying to use R igraph to get x,y coordinates to plot vertices in another 
application.  The data should show a simple organisation chart, hence the 
desire for a top-down tree.

My data set can be found here: 
https://dl.dropbox.com/u/80762057/RelationshipData.csv

I read this csv as a data.frame which I call RelationshipData

I then graph this using: 

> gdf<-graph.data.frame(RelationshipData)

Which gives the warning message:

In graph.data.frame(RelationshipData) :
  In `d' `NA' elements were replaced with string "NA"

As my first ID hasn't got a manager ID (because he's the boss) and therefore no 
edge relationship I remove this line:

> gdf<-gdf-c("NA")

plotting I get a radial tree which is correct.  E(gdf) is also correct.

From the notes I understand that layout.reingold.tilford is the correct 
algorithm to provide the coordinates for a traditional tree:

> l<-layout.reingold.tilford(gdf)

Looking at l I get something similar to:

               [,1]          [,2]
 [1,]   0.000000e+00 2.116259e+214
 [2,]   0.000000e+00 2.116259e+214
 [3,]  3.239144e-319 2.116259e+214
 [4,]   0.000000e+00 2.116259e+214
 [5,]  8.156530e-320 2.116259e+214
 [6,]  6.147313e+257  0.000000e+00

(top lines only) which isn't what I'm expecting.

When I plot this using

> plot(gdf,l)

I get the warning message:

In if (axes) { :
  the condition has length > 1 and only the first element will be used

and the same radial tree.

What am I doing wrong?

Thanks in advance

Andrew