Selecting clusters based on number of nodes iGraph/R

Question

Is there a way to select a subgraph/subset where clusters have maximum number of vertices?

Essentially I want to do something like:

want <- components(X)$csize < 20  

I thought about merging the cluster id's from the graph data frame to the node df, then using a count, or something similar, to subset the original df and compute the graph data frame again.

Answer 1

Here is a potential solution using a random graph. You will need to use groups on the components to identify which nodes belong to which components , then you will need to use length to identify how big the components are:

set.seed(4321)
g <- sample_gnm(100, 40, F, F)
plot(g, vertex.size = 5, vertex.label = '')

want <- g %>%
  components %>%
  groups %>%
  .[sapply(., length) > 3]

want will provide the following:

$`1`
[1]  1 34 38 45 75

$`3`
 [1]   3  12  24  39  50  54  58  60  67  84  97  99 100

$`5`
[1]  5 35 37 41 44 53 65 90

Then you can remove all nodes that aren't included in want

newG <- g %>%
  {. - V(.)[! as.numeric(V(.)) %in% unlist(want)]}

plot(newG, vertex.size = 5, vertex.label = '')