How to identify multiple independent subgraphs and assign its corresponding subgraph to each node in-CodePudding

I have a problem with network data in R. Suppose I have a graph that looks like this:

library(igraph)
a1=data.frame(A=c(1,1,2,2,3,7,9,10),B=c(2,3,4,5,6,8,8,11))
a2=graph_from_data_frame(a1, directed = F)
plot(a2)

I can see that there are three independent subgraphs, and nodes 1 to 6 belong to subgraph 1, nodes 7 to 9 belong to subgraph 2, and nodes 10 and 11 belong to subgraph 3.

a3=data.frame(node=c(1:11),sub=c(1,1,1,1,1,1,2,2,2,3,3))

I want to output a table like a3, and is there direct code to do this assignment in R?

CodePudding user response：

Here is a solution.

sub <- clusters(a2)$membership
a3 <- data.frame(node = names(sub), sub)
a3 <- a3[order(as.integer(a3$node)), ]
a3

An alternative:

cmp <- components(a2)
data.frame(node = unlist(groups(cmp)), 
           sub = sort(as.integer(cmp$membership)))

CodePudding user response：

Another option using decompose

> Map(
    function(x, y) data.frame(node = names(V(x)), sub = y),
    d <- decompose(a2),
    seq_along(d)
  )
[[1]]
  node sub
1    1   1
2    2   1
3    3   1
4    4   1
5    5   1
6    6   1

[[2]]
  node sub
1    7   2
2    9   2
3    8   2

[[3]]
  node sub
1   10   3
2   11   3