From list to adjacency matrix

问题

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

回答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

回答2:

I suspect something like this is what you are looking for:

# Input
my_list <- list(1, 4, 1, 2, 2, 3, 2, 5, 1, 2, 3, 7, 3, 4, 3, 5, 1, 1, 4, 6)

# Make to vector
my_list <- unlist(my_list)

# Number of vertices in graph (may change this to any number > max(my_list))
num_vertices <- max(my_list)

# Number of edges
num_edges <- length(my_list) / 2

# Transform edge data into data.frame, each row is an edge
edges <- data.frame(tails = my_list[rep(c(TRUE, FALSE), num_edges)],
                    heads = my_list[!rep(c(TRUE, FALSE), num_edges)])

# Count duplicate edges (if multi-edges should not be allowed, set count to 1)
edges$count <- ave(rep(1, num_edges), edges, FUN = base::sum)

# Remove duplicate edges, count encodes multi-edges
edges <- edges[!duplicated(edges), ]

# Make empty adjacency matrix
adjacency_matrix <- matrix(0, ncol = num_vertices, nrow = num_vertices)

# Populate matrix
adjacency_matrix[as.matrix(edges[, c("heads", "tails")])] <- edges$count

# Make graph undirected
adjacency_matrix <- adjacency_matrix + t(adjacency_matrix) - diag(diag(adjacency_matrix))

Btw, list may not be the best name for a list.

来源：https://stackoverflow.com/questions/36378237/from-list-to-adjacency-matrix

标签

adjacency-matrix