Replacing off-diagonal elements with a fixed value

I have a square matrix and now I want to replace all its off-diagonal elements with a fixed value. Some approaches how this can be done are discussed in Replacing non-diagonal elements in a matrix in R (hopefully a better asked this time)

For example,

m <- matrix(c(1,2,3,4,3,9,5,5,8),ncol=3)
m[upper.tri(m) | lower.tri(m)] <- 999
m

I am wondering if the step can be performed using dplyr chain rule, something like

library(dplyr)
matrix(c(1,2,3,4,3,9,5,5,8),ncol=3) %>%
 ### add this -> m[upper.tri(m) | lower.tri(m)] <- 999

Any pointer will be very helpful

>Solution :

You can use the mutate function in dplyr to modify the elements of the matrix. Here is an example of how you can do this:

library(dplyr)

m <- matrix(c(1,2,3,4,3,9,5,5,8), ncol = 3)

m %>%
  mutate(m = ifelse(upper.tri(m) | lower.tri(m), 999, m))

This will create a new matrix with the same dimensions as m but with the off-diagonal elements replaced by 999.

Alternatively, you can use the replace function to directly modify the original matrix m:

m[upper.tri(m) | lower.tri(m)] <- 999

This will modify the original matrix m in place and replace the off-diagonal elements with 999.