How to create a directed network from a matrix?

Say that we have such a matrix:

The 1 indicates a direction from the row to the column, a 2 means a bi-direction, a zero no-relationship (diagonal is by default always 0). I would like then to build a network that represents these relationships, so, for example, one-side arrow from D to A, two-side arrow between A and B, and so on. How to do this using the library igraph?

Solution

You can turn your (custom?) graph representation to adjacency matrix by replacing twos with ones, from there it's just igraph::graph_from_adjacency_matrix()

library(igraph)
m <- matrix(c(0,2,1,0,
              2,0,0,0,
              0,1,0,1,
              1,0,0,0),
            nrow = 4, byrow = TRUE,
            dimnames = list(LETTERS[1:4],LETTERS[1:4]))
m
#>   A B C D
#> A 0 2 1 0
#> B 2 0 0 0
#> C 0 1 0 1
#> D 1 0 0 0

# relpace 2s with 1s and you'll have adjacency matrix
m[m == 2] <- 1
m      
#>   A B C D
#> A 0 1 1 0
#> B 1 0 0 0
#> C 0 1 0 1
#> D 1 0 0 0

plot(graph_from_adjacency_matrix(m))

^{Created on 2024-06-02 with reprex v2.1.0}