R: Trim characters other than whitespace from a string

Question

In R, if you want to trim all whitespace characters from the end of a string, you'd do trimws(to.be.trimmed, "right"), like so:

> trimws("nauris        ", "right")
[1] "nauris"

What if instead of trimming out whitespace characters, I'd want to trim periods (or some other characters)? In Python, you'd do string.rstrip(char). Here's some desired outputs:

> rstrip("nauris", "s")
[1] "nauri"
> rstrip("nauris.", ".")
[1] "nauris"
> rstrip("nauris....", ".")
[1] "nauris"
> rstrip("stack", "c")
[1] "stack"

Giving said period as the last argument does not work as it just returns an empty string:

trimws("nauris.", "right", ".")
[1] ""

Is it always the same character each time you are trimming? Would that character appear elsewhere in any of the strings? — Jaccar, Jun 19 '19 at 10:08
gsub removes those characters from the middle of the string as well, for example gsub('\\c', '', "stack") returns "stak" instead of "stack". — hilssu, Jun 19 '19 at 10:10
Related to https://stackoverflow.com/questions/53754273/extract-characters-bound-by-parentheses/53754556#53754556 — akrun, Jun 19 '19 at 15:08

Ritchie Sacramento · Accepted Answer · 2019-06-19T10:32:13.993

6

From R version 3.6.0 trimws() has a whitespace argument so you can do:

trimws("nauris", "right", whitespace = "s")
[1] "nauri"

trimws("nauris.....", "right", whitespace = "\\.")
[1] "nauris"

The documentation states that internally trimws() uses sub(re, "", *, perl = TRUE) so special characters need to be escaped.

edited Jun 19 '19 at 10:32

answered Jun 19 '19 at 10:12

Ritchie Sacramento

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It's worth of mentioning that the `whitespace` argument is available since `R-3.6.0`. – tmfmnk Jun 19 '19 at 10:15
What version is that? I get an error about unused argument – Sotos Jun 19 '19 at 10:15
@tmfmnk - thank you. Have updated the post to include the version it was introduced. – Ritchie Sacramento Jun 19 '19 at 10:18

score 1 · Answer 2 · answered Jun 19 '19 at 10:18

For people who haven't updated R yet (like me), you can copy the trimws function and change it according to our requirement.

trim_periods <- function (x, which = c("both", "left", "right")) {
   which <- match.arg(which)
   mysub <- function(re, x) sub(re, "", x, perl = TRUE)
  if (which == "left") 
     return(mysub("^[.]+", x))
   if (which == "right") 
      return(mysub("[.]+$", x))
   mysub("[.]+$", mysub("^[.]+", x))
}

trim_periods("...abc..def..", "right")
#[1] "...abc..def"

trim_periods("...abc..def..")
#[1] "abc..def"

R: Trim characters other than whitespace from a string

2 Answers2