What is the right way in R to iterate over a multidimensional array and compare it's elements?

Question

I am trying to implement Floyd Warshall's algorithm in R. When I run the programm I get the following error: Error in if ((graph[i][k] + graph[k][j]) < graph[i][j]) { : argument is of length zero

I know this has something to do with the iteration over graph array. What is the right way to iterate over graph array? Thank you.

Graph:

       10
   (0)------->(3)
    |         /|\
  5 |          |
    |          | 1
   \|/         |
   (1)------->(2)
        3

Code:

inf <- 99999 
graph <- array(c(0, inf, inf, inf, 5, 0, inf, inf, inf, 3, 0, inf, 10, inf, 1, 0), dim = c(4, 4, 1))

V <- 4

new.floyd <- function(graph){
  k <- 0
  i <- 0
  j <- 0
  
  while(k < V){ 
    while(i < V){
      while(j < V){
        if((graph[i][k] + graph[k][j]) < graph[i][j]){
          graph[i][j] <- (graph[i][k] + graph[k][j])
        }
        j <- j + 1
      }
      j <- 0
      i <- i + 1
    }
    i <- 0
    k <- k + 1
}

Your indexing is wrong: use graph[i,k,] not graph[i][k]. — user2554330
– user2554330, Commented Jul 4, 2020 at 16:42
@user2554330 Thank you. I fixed it but now I am getting: Error in if(..) argument is of length zero. — C96
– C96, Commented Jul 6, 2020 at 16:08

C96 · Accepted Answer · 2020-07-06 16:54:24Z

0

inf <- 99999 
graph <- array(c(0, inf, inf, inf, 5, 0, inf, inf, inf, 3, 0, inf, 10, inf, 1, 0), dim = c(4, 4, 1))

V <- 4

new.floyd <- function(graph){
  k <- 1
  i <- 1
  j <- 1
  
  while(k <= V){ 
    while(i <= V){
      while(j <= V){
        if((graph[i, k,] + graph[k,j,]) < graph[i,j,]){
          graph[i,j,] <- (graph[i,k,] + graph[k,j,])
        }
        j <- j + 1
      }
      j <- 1
      i <- i + 1
    }
    i <- 1
    k <- k + 1
}
 
  print(graph)

  
}

new.floyd(graph)

answered Jul 6, 2020 at 16:54

C96

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