R (igraph): orientation of edge beginning and ending from same vertex

user_9371768 0
Viewed 914

I want to change the orientation of the edges that start and end at the same vertex. When I use plot.igraph, these edges are all facing right, which means the vertices that are on the left side of the circle, will have their edge overlap on other edges. Does anyone know how we can control their directions, for example point to the outside of the circle? Below is the actual figure I want to edit.

Example of problem

A small example if you want to play around with is posted below:

library(igraph)
g <- data.frame(start=c("a","a","b","b", "c", "c"), end=c("a","b","b","c", "c", "a"))
graph <- graph.data.frame(g, directed = T)
plot(graph, layout = layout.circle(graph))

enter image description here

igraph r
2 Answers

You can control this with the parameter edge.loop.angle.
See the help page ?igraph.plotting

plot(graph, layout = layout.circle(graph), 
     edge.loop.angle=c(0,0,4*pi/3,0, 2*pi/3,0))

Graph with angled loops

Note that you need an angle for all edges, not just the loops, even though this only applies to loops. Also, it appears that the angle gives the amount of clockwise rotation from the horizontal.

user_47526750

The problem is that all the edges have to be referenced, which made a large network hard to work with. This seems to work:

edgeloopAngles <- numeric(0)
b <- 1
M <- matrixSize
m <- 0

for(row in 1:nrow(myMatrix)) {
    for(col in 1:ncol(myMatrix)) {
        if (row == col) {
            m <- m+1
        }
        if (myMatrix[row,col] > 0) {
            edgeloopAngles[[b]] <- 0

            if (row == col) {
                edgeloopAngles[[b]] <- (2 * pi * (M - m) / M)
            }
            b <- b+1
        }
    }
}

Then when you call the igraph, use it like this:

plot(g, layout=star, vertex.label.cex=0.75, vertex.label.family="sans", edge.curved = T,  vertex.size=15, edge.arrow.size=0.5, edge.width=E(g)$weight, edge.loop.angle=edgeloopAngles, main="Graph Name")
user_132943350
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