how to store result in list from a for loop

Question

I'm new to R, this may be a silly question, but I don't know how to resolve.

I have a for loop which will return possibly i*j non-empty elements.

I want to store all the non-empty result in a list, but if I use result[[i]]<-tmp in the loop, it can only store up to i elements, how am I able to store all values in a list? Thanks

  result<-list()
  for (i in 1:nrow(m)){
    for (j in 1:i){
      if(m[i,j]!=0 && m[j,i]!=0){
        num=min(m[i,j],m[j,i])
        tmp=c(i,j,num)
        result[[i]]<-tmp
      }
    }
  }

sample data
set.seed(123)
m= matrix(sample(0:5, size = 5*5, replace = TRUE), ncol = 5)

Desired

 row col min
[1] 1 1 1
[1] 2 2 3
[1] 3 1 2
[1] 3 2 2
[1] 3 3 4
[1] 4 1 5
[1] 4 2 1
[1] 4 4 1
[1] 5 1 5
[1] 5 2 2
[1] 5 4 5
[1] 5 5 3

Per David's answer

pmin(mx[upper.tri(mx, diag = TRUE)], mx[lower.tri(mx, diag = TRUE)])

[1] 1 0 2 5 2 3 5 1 0 1 3 0 1 5 3

returns

      > result
[[1]]
[1] 1 1 2

[[2]]
[1] 2 2 3

[[3]]
[1] 3 3 4

[[4]]
[1] 4 4 2

[[5]]
[1] 5 5 4

Answer 1

Here's something like @DavidArenburg's answer (converted from a comment):

idx <- which(upper.tri(m,diag=TRUE),arr.ind=TRUE)
v   <- pmin(m[idx], m[idx[,2:1]])

cbind(idx,min=v)[v>0,]

which gives

      row col min
 [1,]   1   1   1
 [2,]   2   2   3
 [3,]   1   3   2
 [4,]   2   3   2
 [5,]   3   3   4
 [6,]   1   4   5
 [7,]   2   4   1
 [8,]   4   4   1
 [9,]   1   5   5
[10,]   2   5   2
[11,]   4   5   5
[12,]   5   5   3