Re: [igraph] Upside-Down Trees and Vertex Size

[Gabor Csardi]

Aaron,

On Wed, Jul 23, 2008 at 01:26:50PM -0700, Aaron Arvey wrote:
> Hi,
>
> First, thanks for the great network library!
>
> Second, I'm trying to create a tree similar to the one found at:
>
> http://en.wikipedia.org/wiki/Alternating_decision_tree
>
> I've figured out the basic ways of specifying attributes in R, (e.g.  
> V(g)$shape <- "rectangle"); however there are a few things that I can't  
> seem to figure out.

hmmm, you don't have to "figure out", it is documented in 
?igraph.plotting.

>   * I'm plotting the graph using the layout.reingold.tilford layout.
>     However, I wanted to have the root at the top instead of the bottom.
>     Is there an easy way to specify this or do I need to dig into the code
>     and create an option?

There is no need for such an option, just do something like

coords <- layout.reingold.tilford(g)
coords[,2] <- max(coords[,2])-coords[,2]

>   * I'm use larger labels than are normally used with the package.  As
>     such, I'm attempting to set the size of the node appropriately, since
>     it is not automatically resized for the given text.  I'm currently
>     using a few hacks, but nothing serious.  Does anyone have any
>     suggestions for robustly resizing vertices to be compatible with
>     arbitrary text?

1) create an empty plot
2) use strwidth() to measure the width of the text expressions
3) use 'vertex.size'*100 (nasty internal thing in igraph) and
   'add=TRUE' to plot the graph.

E.g.

plot(1, type="n", axes=FALSE, xlab=NA, ylab=NA, xlim=c(-1,1), ylim=c(-1,1))
g <- graph.ring(10)
V(g)$label <- sample( c("Hi!", "Hello!", "Hello world!"), vcount(g), rep=TRUE)
sw <- strwidth(paste("", V(g)$label, ""))
sh <- max(strheight(V(g)$label))
plot(g, vertex.shape="rectangle", add=TRUE, vertex.size=sw*100,
     layout=layout.circle, vertex.size2=sh*100*2)

The paste() just leaves some space on the sides. You might need to use
layout.norm to fit your layout into the (-1,1) region.

>   * I noticed that plotting a large tree using the postscript device in R
>     gives a fairly difficult to read output (e.g plot(graph.tree(1000, 2)))
>     Is there an easy way to resize the page so that the tree can be more
>     spread out?

You can set the page size with the 'width' and 'height' options of 
'postscript().

Gabor

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> Any advise is greatly appreciated!
>
> Thanks,
>
> Aaron
>
>
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-- 
Csardi Gabor <address@hidden>    UNIL DGM