Edges from matching column values in R

Question

I would like to create an edge from matching column values in a table, so basically:

   V1  V2  V3
A  1    1   0
B  1    0   1
C  0    1   1
D  1    0   1

if I had a table like so, then I would like to make an edge list where

A - B
A - D
A - C
B - C
B - D

so I would like to create an edge whenever the column values match per row. I've looked over a lot of documentation but I can't seem to figure out anything that does something similar to this. Any help would be appreciated!

Answer 1

I would try the "igraph" package after using crossprod on your data. Assuming your data.frame is called "mydf":

out <- crossprod(t(mydf))
out[lower.tri(out, diag=TRUE)] <- 0

library(igraph)
g <- graph.adjacency(out)
get.edgelist(g)
#      [,1] [,2]
# [1,] "A"  "B" 
# [2,] "A"  "C" 
# [3,] "A"  "D" 
# [4,] "B"  "C" 
# [5,] "B"  "D" 
# [6,] "B"  "D" 
# [7,] "C"  "D" 

If you don't want duplicates, you can use:

g <- graph.adjacency(out > 0)
get.edgelist(g)