Krzysiek Krzysiek - 1 month ago 9
R Question

Drawing graph G=(V,E) in R

I would like to draw standard G=(V,E) graph in R either by ggplot or some R built-in functions.

I have a data frame containing vertices coords:

> V
x y
1 589.3438 6422.883
2 8762.6921 7789.147
3 7973.0883 4552.745
4 4100.8408 8108.702
5 6049.3329 6547.239


and a zero-one symetric matrix representing edges:

> E
[,1] [,2] [,3] [,4] [,5]
[1,] 0 0 0 1 0
[2,] 0 0 1 0 1
[3,] 0 1 0 0 1
[4,] 1 0 0 0 1
[5,] 0 1 1 1 0


I plot vertices using:

plotGraph <- function() {
qplot(x,
y,
data=V,
xlim=c(0,SIZE),
ylim=c(0,SIZE),
main="Graph"
)
}


How could I draw graph edges on the same plot? Or how do I plot a single edge from (x1, y1) to (x2, y2)?

Any help would be appreciated.

Answer

If using igraph is an option, I would recommend it. It's a very useful package when working with graphs. Here's how I would do it using igraph:

library(igraph)

# convert V and E to matrices
V <- data.matrix(V)
g <- graph_from_adjacency_matrix(E, mode="undirected")

plot.igraph(g, layout = V)

igraph output

Alternatively, if you want a ggplot-flavored method, you can use ggnet2 from the GGally package:

library(GGally)

V <- data.matrix(V)
# with ggnet2 you don't have to convert E to a graph

ggnet2(net = E, mode = V ) 

ggnet2 output