R Keep colnames and rownames when using sapply on a matrix

Question

A question was already asked on how keeping colnames in a matrix when applying apply, sapply, etc. here. But I didn't find how to keep the column AND row names of a matrix.

Below an example:

mat = matrix(c(as.character(1:4)), nrow = 2)
colnames(mat) = c( 'col1', 'col2' )
rownames(mat) = c( 'row1', 'row2' )
mat = apply(mat,  2,  function(x) as.numeric(paste(x)))
colnames(mat)
rownames(mat)

Thanks in advance :-)

[this](https://stackoverflow.com/questions/15229199/r-rownames-colnames-dimnames-and-names-in-apply) question and it's answer might be worth taking a look at — Humpelstielzchen, Sep 25 '19 at 12:37

score 5 · Accepted Answer · answered Sep 25 '19 at 12:34

5

We can wrap your application in a user-defined function.

mat_fun <- function(m){
  m2 <- apply(m,  2,  function(x) as.numeric(paste(x)))
  colnames(m2) <- colnames(m)
  rownames(m2) <- rownames(m)
  return(m2)
}

mat_fun(mat)
#      col1 col2
# row1    1    3
# row2    2    4

answered Sep 25 '19 at 12:34

www

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1

Very clever! He had to think. Thank you very much ;-) – Flora Grappelli Sep 25 '19 at 13:10

score 1 · Answer 2 · answered Sep 25 '19 at 13:16

1

If you reassign using [], the names are preserved. Unfortunately, this is only useful when you don't want to create a new matrix and also don't want to change the class of the elements (e.g. from character to numeric as in this example)

mat[] <- apply(mat,  2,  function(x) 1 + as.numeric(paste(x)))
mat
#      col1 col2
# row1 "2"  "4" 
# row2 "3"  "5"

answered Sep 25 '19 at 13:16

IceCreamToucan

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Thanks for this precision. This method may be very useful on some operations. – Flora Grappelli Sep 25 '19 at 13:25

R Keep colnames and rownames when using sapply on a matrix

2 Answers2