Is there a way to do a random sample of a matrix to get cell location in R?

(I’m a beginner in R so sorry if this makes no sense)If I have a 3x3 matrix called M and I want to take a sample to get a random cell location, how would I do that? For example when I do sample(M,size=1,replace=FALSE) it gives me a random number from the matrix but I want it to give me the location of the number in the form of let’s say M[1,2] for example.

Solution

Suppose your matrix is like this:

M <- matrix(1:9, 3)

M
#>      [,1] [,2] [,3]
#> [1,]    1    4    7
#> [2,]    2    5    8
#> [3,]    3    6    9

Then you can sample across rows and columns independently:

set.seed(1)

cell_index <- t(c(row = sample(nrow(M), 1), column = sample(ncol(M), 1)))

cell_index
#>      row column
#> [1,]   1      3

which allows

M[cell_index]
#> [1] 7

^{Created on 2022-10-09 with reprex v2.0.2}