From list to adjacency matrix

Question

I have a list like that:

> print(list)
[[1]]
[1] 1

[[2]]
[1] 4

[[3]]
[1] 1

[[4]]
[1] 2

[[5]]
[1] 2

[[6]]
[1] 3

[[7]]
[1] 2

[[8]]
[1] 5

[[9]]
[1] 1

[[10]]
[1] 2

[[11]]
[1] 3

[[12]]
[1] 7

[[13]]
[1] 3

[[14]]
[1] 4

[[15]]
[1] 3

[[16]]
[1] 5

[[17]]
[1] 1

[[18]]
[1] 1

[[19]]
[1] 4

[[20]]
[1] 6

Now I want to turn this list into an adjacency matrix so that I can then build a graph undirect not simple (there may be multilinks and selfloops).

This list should be read in pairs, that is, (1 4) indicates that there is a link from node 1 to node 4, the pair (1 2) indicates that there is a link from node 1 to node 2, etc.

How can I do this?

I thought I iterate the list with a for loop with step = 2 but I haven't found how to do. And I'm not sure how to assign the values of the matrix, what I assing to multilinks?

Thanks a lot

Answer 1

Here's another way

lst <- list(1, 4, 1, 2, 2, 3, 2, 5, 1, 2, 3, 7, 3, 4, 3, 5, 1, 1, 4, 6)
library(igraph)
g <- make_graph(unlist(lst), directed = F)
( m <- as_adjacency_matrix(g, sparse = F) ) 
#      [,1] [,2] [,3] [,4] [,5] [,6] [,7]
# [1,]    1    2    0    1    0    0    0
# [2,]    2    0    1    0    1    0    0
# [3,]    0    1    0    1    1    0    1
# [4,]    1    0    1    0    0    1    0
# [5,]    0    1    1    0    0    0    0
# [6,]    0    0    0    1    0    0    0
# [7,]    0    0    1    0    0    0    0