Color legend not appearing in ggnet2 plot

Question

I am trying to plot the network g:

> g
 Network attributes:
  vertices = 866 
  directed = TRUE 
  hyper = FALSE 
  loops = FALSE 
  multiple = FALSE 
  bipartite = FALSE 
  total edges= 5310 
    missing edges= 0 
    non-missing edges= 5310 

 Vertex attribute names: 
    color degree membership vertex.names 

 Edge attribute names not shown 

g node "membership" occurs with the following frequency:

> table(g %v% "membership")

  1   2   3   4   5 
 19  44  11 196 596 

When I use the excellent ggnet2 package and the following function, a plot without a legend returns, although the documentation suggests a plot for node size, color, etc. is automatically generated (see the node legends section):

ggnet2(g_new, color = "membership", size = "degree") +
    guides(size = F)

Answer 1

My guess is that you are passing a numeric vertex attribute to ggnet2, which then understands it as a vector of color values.

Short answer:

Turn your membership attribute into a character string, and you will be fine.

Long answer:

Compare the two graphs in the example below to get the difference:

library(GGally)
library(ggplot2)
library(network)
library(sna)

g <- network(rgraph(10))
g %v% "membership" <- sample(1:5, 10, replace = TRUE)
g %v% "membership_string" <- as.character(g %v% "membership")
g %v% "degree" <- degree(g)

g
table(g %v% "membership")

## Your graph
ggnet2(g, color = "membership", size = "degree") +
  guides(size = FALSE)

## Your graph, with the membership variable as a string
ggnet2(g, color = "membership_string", size = "degree") +
  guides(size = FALSE)

If you want distinguishable colors instead of grayscale levels in your plot, you probably want something like this:

ggnet2(g, color = "membership_string", size = "degree", color.palette = "Set1") +
  guides(size = FALSE)

Also, may I recommend that you give a try to the ggnetwork package, which has additional functionalities?