Using backreferences with gsub in R

Asked Oct 07 '18 at 14:42

Active Oct 07 '18 at 14:42

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I have a list of strings and I need to change those of them being followed by a certain suffix to being preceded by a certain prefix. I was using gsub and back referencing the the parenthesized subexpression in the pattern argument in the replacement.

The problem is that the function pushes the backreference to the beginning of the output string

> gsub("([:alnum:]*).suff", "\\1", "string.suff")
[1] "string"
> gsub("([:alnum:]*).suff", "pre_\\1", "string.suff")
[1] "stringpre_"

any idea, possibly not involving a workaround via a combination of endsWith, paste and ifelse ?

asked Oct 07 '18 at 14:42

Fra

3

You need double [ like this: `[[:alnum:]]` – G. Grothendieck Oct 07 '18 at 14:56
See https://stackoverflow.com/a/42013383/3832970. If you use `stringr`, you would see another result. – Wiktor Stribiżew Oct 07 '18 at 21:02

Using backreferences with gsub in R

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