I have created a matrix S, which describes a graph. It looks like this:
[,1] [,2] [,3]
1 2 3 9
2 1 10 5
3 9 4 8
4 3 9 7
5 10 4 11
6 11 5 10
7 4 3 8
8 9 3 4
9 3 8 4
10 5 2 11
11 6 5 10
It means that 3rd vertex is connected with 9th, 4th and 8th vertex. My graph is not directed. I would like to create an adjacency matrix. For example the third row would be:
[1,0,0,1,0,0,1,1,1,0,0]
I thought about creating a matrix 11x11 of zeros and analise it row by row. My result matrix should be symmetirc. However I cannot use any loops, "for" is forbidden. I am mathematician and i'm totally new to R. How should I start solving this problem?
Data
S <- structure(c(2L, 1L, 9L, 3L, 10L, 11L, 4L, 9L, 3L, 5L, 6L, 3L,
10L, 4L, 9L, 4L, 5L, 3L, 3L, 8L, 2L, 5L, 9L, 5L, 8L, 7L, 11L,
10L, 8L, 4L, 4L, 11L, 10L), .Dim = c(11L, 3L))
I think you can try the following base R code
v <- rep(0,nrow(S))
C <- t(apply(S,1,function(k) replace(v,k,1)))
res <- +(t(C) + C >0)
which gives the adjacency matrix as
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11]
[1,] 0 1 1 0 0 0 0 0 1 0 0
[2,] 1 0 0 0 1 0 0 0 0 1 0
[3,] 1 0 0 1 0 0 1 1 1 0 0
[4,] 0 0 1 0 1 0 1 1 1 0 0
[5,] 0 1 0 1 0 1 0 0 0 1 1
[6,] 0 0 0 0 1 0 0 0 0 1 1
[7,] 0 0 1 1 0 0 0 1 0 0 0
[8,] 0 0 1 1 0 0 1 0 1 0 0
[9,] 1 0 1 1 0 0 0 1 0 0 0
[10,] 0 1 0 0 1 1 0 0 0 0 1
[11,] 0 0 0 0 1 1 0 0 0 1 0
If you would like to use igraph, here is another option
library(igraph)
df <- data.frame(from = rep(1:nrow(S), each = ncol(S)), to = c(t(S)))
res <- as_adjacency_matrix(
simplify(
graph_from_data_frame(
df,
directed = FALSE
)
),
sparse = FALSE
)
which gives
1 2 3 4 5 6 7 8 9 10 11
1 0 1 1 0 0 0 0 0 1 0 0
2 1 0 0 0 1 0 0 0 0 1 0
3 1 0 0 1 0 0 1 1 1 0 0
4 0 0 1 0 1 0 1 1 1 0 0
5 0 1 0 1 0 1 0 0 0 1 1
6 0 0 0 0 1 0 0 0 0 1 1
7 0 0 1 1 0 0 0 1 0 0 0
8 0 0 1 1 0 0 1 0 1 0 0
9 1 0 1 1 0 0 0 1 0 0 0
10 0 1 0 0 1 1 0 0 0 0 1
11 0 0 0 0 1 1 0 0 0 1 0