[R] regular expression help

[Gabor Grothendieck]

A backreference is contained in parentheses and there are no parentheses
in your regular expression, hence the error message.

Its probably easiest just to remove all non-letters:

x <- "45x53yy66"
gsub("[^[:alpha:]]", "", x) # xyy

On 4/18/07, Petr PIKAL <petr.pikal at precheza.cz> wrote:
> Dear all
>
> as usual I am again lost in virtues of regular expressions.
>
> I have such character vector named vzor:
>
> [365] "61A"      "62C/27"   "65A/27"   "66C/29"   "69A/29"   "70C/31"
> "73A/31"   "74C/33"   "77A/33"   "81A/35"   "82C/37"   "85A/37"   "86C/39"
>
> [378] "89A/39"   "90C/41"   "93A/41"   "94C/43"   "97A/43"   "98C/45"
> "101A/45"  "102C/47"  "105A/47"  "106C/49"  "109A/49"  "110C/51" "113A/51"
>
>
> and I want only letters from it.
>
> I tried
>
> > gsub("[[:alpha:]]"," \\1",vzor)
> Error in gsub("[[:alpha:]]", " \\1", vzor) :
>        invalid backreference 1 in regular expression
>
> gsub("[:alpha:]"," \\1",vzor)
>
> gives me the same vector
>
> There is probably very simple solution to it which I overlooked and
> examples in help page did not help me to find it.
>
> Thank you
> Best regards
>
> Petr Pikal
> petr.pikal at precheza.cz
>
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