R: change to the same character as the previous character in a string

Question

Suppose I have a vector c('JKA1','BP9C','SSTQ3WA') and I want to change the character before the number to that very number, so that R returns 'JK11' 'B99C' 'SST33WA'. Is there anyway to do this with regex or am I better off using something other than R?

Answer 1

Match the letter before the number and then capture the number through capturing group. Then replace the matched characters with \\1\\1 means double times of characters present inside the group index 1.

> x <- c('JKA1','BP9C','SSTQ3WA')
> gsub("[A-Za-z](\\d)", "\\1\\1", x)
[1] "JK11"    "B99C"    "SST33WA"

sub function would be enough for this case.

> sub("[A-Z](\\d)", "\\1\\1", x)
[1] "JK11"    "B99C"    "SST33WA"