[R] Flummoxed by gsub().

PIKAL Petr petr.pikal at precheza.cz
Wed Aug 23 08:41:31 CEST 2017


Hi Rolf

I am not at all an expert in regex but

gsub("[[:alpha:]]","",x)

Works as you expected. Do not ask me why.

Cheers
Petr


> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Rolf Turner
> Sent: Wednesday, August 23, 2017 7:46 AM
> To: r-help mailing list <r-help at r-project.org>
> Subject: [R] Flummoxed by gsub().
>
>
> I have a vector (say "x") of the form
>
>      [1] "mung5"  "mung10" "mung20" "gorp5"  "gorp10" "gorp20"
>
> I want to extract just the numbers (strings of digits) that appear at the end of
> the strings in "x".
>
> My reading of ?regex led me to believe that
>
>      gsub("[:alpha:]","",x)
>
> should give the result that I want.  However it returns
>
>      [1] "mung5"  "mung10" "mung20" "gor5"   "gor10"  "gor20"
>
> i.e. it chops the last letter out of the "gorp" string, but nothing else.
>
> I am completely bewildered by this behaviour and can see no rationale for it
> nor any way to adjust my syntax to get what I want.
>
> A bit of Googling led me to the information that
>
>      gsub("\\D","",x)
>
> should work, and indeed it does, giving:
>
>      [1] "5"  "10" "20" "5"  "10" "20"
>
> OMMMMM!  (Apparently "\D" means *not* a digit.)
>
> So I have *a* solution to my problem.  However I would really like to know why
> the <expletive deleted> the first idea I tried did not work and what it is actually
> *doing*!
>
> Anybody?
>
> cheers,
>
> Rolf Turner
>
> --
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
>
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