How to rank a vector inside a matrix? in R

Question

I have made a matrix where each element in the matrix is a vector of two numbers. Now I want to rank all the vectors inside, so I get the rank of the vectors as the new vector elements of the matrix.

Here is an example of the code:

listwvectors <- vector("list")
t=1
for (i in 1:3) {
  for (j in 1:5) {
    listwvectors[[t]] <- c(i,j)
    t=t+1
  }
}
print(listwvectors)

testmatrix <- matrix(data=listwvectors, nrow=5, ncol=3)
print(testmatrix)

rank(testmatrix[1,1])

The last part ("rank(testmatrix[1,1])") just give 1. Why is that? I want it to print the ranked vector. So in fact, I want to make a new matrix that has the same mode as the testmatrix but the vectors inside is the ranked vectors of the testmatrix.

Hope you understand what I am trying to ask. Thanks in advance!:)

Hi Monica. Could you add a [minimal reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example/5963610#5963610)? It will make it easier for others to find and test a answer to your question. That way you can help others to help you! — dario, Mar 03 '20 at 10:43
Yes here is an example you can try. listwvectors <- vector("list") t=1 for (i in 1:3) { for (j in 1:5) { listwvectors[[t]] <- c(i,j) t=t+1 } } print(listwvectors) testmatrix <- matrix(data=listwvectors, nrow=5, ncol=3) print(testmatrix) rank(testmatrix[1,1]) — Monica, Mar 03 '20 at 12:15
To answer your question *"Why is that?"*: `testmatrix[1,1]` is a list. Its first element is a vector. If you want to use this first element of the list you have to do : `testmatrix[1,1][[1]]` — jogo, Mar 03 '20 at 12:35
Oh that is so helpful! Thanks a lot! Do you know how I then can go through all the vectors in the testmatrix to get all vectors ranked? I have no idea how i then can make a for loop if i need to use both [1,1] and [1]. What is the next vector in the matrix than? is it [1,1][2] or is it [1,2][1] for example? in other words, is there always [1] in the last bracket? — Monica, Mar 03 '20 at 12:51
to access the content of the i-th element of a list in R we use `[[i]]`, ofr example `rank(testmatrix[1,1][[1]])` returns `[1] 1.5 1.5` — dario, Mar 03 '20 at 12:53
`sapply(testmatrix, rank)` or `array(sapply(testmatrix, rank), dim=c(2, dim(testmatrix)))` — jogo, Mar 03 '20 at 14:30

score -1 · Answer 1 · answered Mar 03 '20 at 12:54

minimal example data:

m <- matrix(list(c(1,3), c(2,1), c(2,2), c(1,2)), ncol=2)

        [, 1]    [, 2]
[1, ] c(1, 3)  c(2, 2) 
[2, ] c(2, 1)  c(1, 2)

Solution 1 using apply (returns '3d matrix'):

apply(apply(m, c(1,2), function(x) rank(x[[1]]))

Solution 2 using loop (returns '2d matrix' of lists):

result <- m # copy original matrix as template to recieve rankings
for (i in seq_along(m[, 1])) {
  for (j in seq_along(m[1, ])) {
    result[i, j][[1]] <- rank(m[i, j][[1]])
  }
}

score -2 · Answer 2 · answered Mar 03 '20 at 10:44

-2

since there is only one vector inside a matrix, you can use rank(my_matrix)

answered Mar 03 '20 at 10:44

Prahlad

118
1
4

what do you mean by only one vector? There are one vector per index in the matrix, so in a 3x3 matrix there are 9 vectors inside it. – Monica Mar 03 '20 at 11:54

How to rank a vector inside a matrix? in R

2 Answers2