Replacing off-diagonal elements with a fixed value-CodePudding

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

CodePudding user response：

If it's for the sake of brevity, you could define apply an anonymous function in your pipeline like so:

matrix(c(1,2,3,4,3,9,5,5,8),ncol=3) %>%
  (\(.) {.[upper.tri(.) | lower.tri(.)] = 999; .})() %>%
## rest of pipeline

Edit shamelessly ~~stealing~~ borrowing from @Maël 's elegant solution:

matrix(c(1,2,3,4,3,9,5,5,8),ncol=3) %>%
  ifelse(row(.) == col(.), ., 999) %>%
## rest of pipeline

(note: does not work with the native pipe operator |>)

CodePudding user response：

With ifelse:

ifelse(row(m) == col(m), m, 999)

CodePudding user response：

We may use

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

-output

      [,1] [,2] [,3]
[1,]    1  999  999
[2,]  999    3  999
[3,]  999  999    8