On Aug 7, 2012, at 3:02 PM, Liviu Andronic <landronim...@gmail.com> wrote:
> On Mon, Aug 6, 2012 at 7:35 PM, Marc Schwartz <marc_schwa...@me.com> wrote:
>> is.letter <- function(x) grepl("[[:alpha:]]", x)
>> is.number <- function(x) grepl("[[:digit:]]", x)
>>
>
> Another follow-up. To test for (non-)alphanumeric one would do the following:
>> x <- c(letters, 1:26, '+', '-', '%^&')
>> x[1:10] <- paste(x[1:10], 1:10, sep='')
>> x
> [1] "a1" "b2" "c3" "d4" "e5" "f6" "g7" "h8" "i9" "j10" "k"
> "l" "m" "n"
> [15] "o" "p" "q" "r" "s" "t" "u" "v" "w" "x" "y"
> "z" "1" "2"
> [29] "3" "4" "5" "6" "7" "8" "9" "10" "11" "12" "13"
> "14" "15" "16"
> [43] "17" "18" "19" "20" "21" "22" "23" "24" "25" "26" "+"
> "-" "%^&"
>> xb <- grepl("[[:alnum:]]",x) ##test for alphanumeric chars
>> x[xb]
> [1] "a1" "b2" "c3" "d4" "e5" "f6" "g7" "h8" "i9" "j10" "k"
> "l" "m" "n"
> [15] "o" "p" "q" "r" "s" "t" "u" "v" "w" "x" "y"
> "z" "1" "2"
> [29] "3" "4" "5" "6" "7" "8" "9" "10" "11" "12" "13"
> "14" "15" "16"
> [43] "17" "18" "19" "20" "21" "22" "23" "24" "25" "26"
>> xb <- grepl("[[:punct:]]",x) ##test for non-alphanumeric chars
>> x[xb]
> [1] "+" "-" "%^&"
That will get you values where punctuation characters are used, but there may
be other non-alphanumeric characters in the vector. There may be ASCII control
codes, tabs, newlines, CR, LF, spaces, etc. which would not be found by using
[:punct:].
For example:
> grepl("[[:punct:]]", " ")
[1] FALSE
If you want to explicitly look for non-alphanumeric characters, you would be
better off using a negation of [:alnum:] such as:
grepl("[^[:alnum:]]", x)
or
!grepl("[[:alnum:]]", x)
Regards,
Marc
>
> More regex rules are available on the Wiki [1]. Regards
> Liviu
>
> [1] http://en.wikipedia.org/wiki/Regular_expression
>
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