Replace maximum value of each column

Question

I have a matrix where I want to replace maximum value of each column by -1. How can I do it in R? I tried,

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 set.seed(14)
 mat<- matrix(sample(10,20,replace=TRUE),nr=5)
 apply(mat,2,which.max)
 [1] 3 2 1 4

I don't know how to replace the matrix. How do I deal with duplicate max value within column? Thanks.

Answer 1

Try:

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 mat[which(apply(mat, 2, function(x) x == max(x,na.rm=TRUE)))] <- -1