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rmatrixequality-operator

R: Comparing all numbers in a list to themselves and return a matrix of TRUE/FALSE

Hi all I have numerical vector x <- c(1,2,3,3)

and I want to compare all numbers to each other and return a 4 x 4 matrix of TRUE and FALSE indicating if they are identical or not.

Tried to use loops but have not been successful:

matx <- matrix(FALSE,nrow=length(x),ncol=length(x))
for(i in nrow(matx)) {
  for (j in ncol(matx)) {
    matx[x==x[i],] <- TRUE
  }
}
Solution

  • outer is clearly the way to go. But if you want to use a loop, you need to define your iterators correctly:

    x <- c(1,2,3,3)
N <- length(x)
comp = matrix(, nrow=N, ncol=N)

for(i in 1:N) {
    for(j in 1:N) {
        comp[i, j] = (x[i] == x[j])
    }
}
comp

TRUE    FALSE   FALSE   FALSE
FALSE   TRUE    FALSE   FALSE
FALSE   FALSE   TRUE    FALSE
FALSE   FALSE   FALSE   TRUE