In igraph in R, is it possible to create dotted lines around the vertex objects?

Question

In igraph in R, I currently have a graph looking like:

which was made from the code:

g <- make_undirected_graph(edges = c(1, 3, 2, 1, 2, 4, 3, 4, 4, 5), n = 5)

I would like to instead have dotted lines on the vertices, which are circles. There is an edge.label option, but no vertex.label option. Is there another way to do this? thanks.

Answer 1

You can define your own shapes: https://igraph.org/r/doc/shapes.html and an example of a point with a dotted border is given at https://r.789695.n4.nabble.com/Drawing-a-dotted-circle-td4655331.html. A full example of creating a new shape given at https://lists.gnu.org/archive/html/igraph-help/2013-03/msg00030.html. Also see more examples at ?add_shape. The example below tweaks the code from lists.gnu.org to combine everything.

Function to create new igraph shape

myimg <- function(coords, v=NULL, params) {
  vertex.color <- params("vertex", "color")
  if (length(vertex.color) != 1 && !is.null(v)) {
    vertex.color <- vertex.color[v]
  }
  vertex.size  <- 1/200 * params("vertex", "size")
  if (length(vertex.size) != 1 && !is.null(v)) {
    vertex.size <- vertex.size[v]
  }
  vertex.frame.color <- params("vertex", "frame.color")
  if (length(vertex.frame.color) != 1 && !is.null(v)) {
    vertex.frame.color <- vertex.frame.color[v]
  }
  vertex.frame.width <- params("vertex", "frame.width")
  if (length(vertex.frame.width) != 1 && !is.null(v)) {
    vertex.frame.width <- vertex.frame.width[v]
  }
  ltype <- params("vertex", "ltype")
  if (length(ltype) != 1 && !is.null(v)) {
    ltype <- ltype[v]
  }   

  mapply(coords[,1], coords[,2], vertex.color, vertex.frame.color,
         vertex.size, vertex.frame.width, ltype, 
         FUN=function(x, y, bg, fg, size, lwd, lty) {
           symbols(x=x, y=y, bg=bg, fg=fg, lwd=lwd, lty=lty,
                   circles=size, add=TRUE, inches=FALSE)
         })
  }

You then make igraph recognise the shape using add_shape. You set default parameter values using the parameters argument.

library(igraph)

g <- make_undirected_graph(edges = c(1, 3, 2, 1, 2, 4, 3, 4, 4, 5), n = 5)

add_shape("myimg",  plot=myimg, 
          parameters = list(
            vertex.frame.color=1, 
            vertex.frame.width=1,
            vertex.ltype=1))

Then plot

plot(g,  vertex.shape="myimg", 
         vertex.frame.color=1:5, 
         vertex.frame.width=5, 
         vertex.ltype=1:5,
         vertex.color=6:10,
         vertex.size=seq(50, 80, length=5))

To get all the borders dotted just use vertex.ltype="dotted" or vertex.ltype=3.

Answer 2

I'm not sure how to do this within igraph, but one option would be to print it using ggraph, a package that bridges igraph with ggplot2. Then we can build up the graph in layers and specify the appearance of each one:

library(ggraph)
ggraph(g) +
  geom_edge_link(color = "gray60") +
  geom_node_circle(aes(r = 0.1), lty = "dashed", fill = "orange") +
  geom_node_text(aes(label = ggraph.orig_index)) +
  coord_equal() +
  theme_void()

Answer 3

I don't use igraph but I found the network package a good replacement of it, and it's plotting function is more intuitive (if you are familiar with the base plot parameters) and easier to customize. But I am 100% sure you could find a similar function in igraph that lets you adjust the plot parameters.

require(network)

# build the network
g = as.network.matrix(x = matrix(c(1, 3, 2, 1, 2, 4, 3, 4, 4, 5), nrow = 5, byrow = T), matrix.type = 'edgelist', directed = F)

# vertex.lty is the parameter you are looking for, and you can pass an array to it.
# lty = 2 for dashed lines and lty = 3 for dotted lines.
plot(g, label = 1:5, label.pos = 5, 
     vertex.cex =6, vertex.col = "#ffdd88",
     vertex.lty = c(1,2,2,3,3), vertex.lwd = c(2,3,4,2,3)) 

(Edited for better formatting.)