Plotting directed multigraphs in R

Question

I've never used any graph plotting package in R, I'm familiar with basic plotting commands and with ggplot2 package. What I've found (but not tried out yet) are Rgraphviz, network and igraph packages. So I'd like to ask you, which package has simplest learning curve and satisfies following requirements:

• Has simple layout engines (spring layout, random, ...)
• Tries to draw multiple edges between two vertices so that they would not overlap. As a bonus it would be nice to being able to adjust this.
• Can draw loops.
• Vertex and edge labels, vertex and edge size and color are adjustable.
• (No need for any of the graph algorithms like link analysis, shortest path, max flow etc, but nice, if present)

Answer 1

The igraph package seems to fulfill your requirements, with the tkplot() function helping adjusting the final layout if needed.

Here is an example of use:

s <- cbind(A=sample(letters[1:4], 100, replace=TRUE),
           B=sample(letters[1:2], 100, replace=TRUE))
s.tab <- table(s[,1], s[,2])
library(igraph)
s.g <- graph.incidence(s.tab, weighted=T)
plot(s.g, layout=layout.circle, 
     vertex.label=c(letters[1:4],letters[2:1]),     
     vertex.color=c(rep("red",4),rep("blue",2)), 
     edge.width=c(s.tab)/3, vertex.size=20, 
     vertex.label.cex=3, vertex.label.color="white")

With the interactive display (there's a possibility of using rgl for 3D display), it looks like (I have slightly moved one vertex afterwards):

tkplot(s.g, layout=layout.circle, vertex.color=c(rep("red",4),rep("blue",2)))

Finally, you can even export you graph into most common format, like dot for graphviz.

Answer 2

The multigraph R package can be useful as well. For the above example bmgraph plots such graph:

library("multigraph")
bmgraph(s.tab, layout = "circ", pch = 16:16, pos = 0, vcol = 6:7, lwd = 3, cex = 9)

And for a directed version:

bmgraph(s.tab, "circ", pch = 16:16, pos = 0, vcol = 6:7, lwd = 3, cex = 9, directed = TRUE)