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,

 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.

akrun · Accepted Answer · 2014-06-13T12:26:52.553

7

Try:

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

edited Jun 13 '14 at 12:26

answered Jun 13 '14 at 11:55

akrun

I'd use `==`, not `%in%`. It's faster. – jbaums Jun 13 '14 at 12:15
Is there a "row" version of this? – Tom Nov 16 '19 at 16:46
@Tom It is an old post. If you need the same syntax, may be change `apply(mat, 2` to `apply(mat, 1`. Or another option is `library(matrixStats); mat[mat == rowMaxs(mat)] <- -1` – akrun Nov 16 '19 at 17:44

1 Answers1