Note that you can also do logical comparisons with the results of grepl like:
grepl('^as', a) | grepl('^df',a)
For the given example it is probably simplest to do it in the regular
expression as shown, but for some more complex cases (or including
other variables) the logic with the output may be simpler.
On Tue, Feb 14, 2012 at 8:23 AM, Johannes Radinger <[email protected]> wrote:
>
>
> -------- Original-Nachricht --------
>> Datum: Tue, 14 Feb 2012 10:18:33 -0500
>> Von: Sarah Goslee <[email protected]>
>> An: Johannes Radinger <[email protected]>
>> CC: [email protected]
>> Betreff: Re: [R] Wildcard for indexing?
>
>> Hi,
>>
>> You should probably do a bit of reading about regular expressions, but
>> here's one way:
>>
>> On Tue, Feb 14, 2012 at 10:10 AM, Johannes Radinger <[email protected]>
>> wrote:
>> > Hi,
>> >
>> > -------- Original-Nachricht --------
>> >> Datum: Tue, 14 Feb 2012 09:59:39 -0500
>> >> Von: "R. Michael Weylandt" <[email protected]>
>> >> An: Johannes Radinger <[email protected]>
>> >> CC: [email protected]
>> >> Betreff: Re: [R] Wildcard for indexing?
>> >
>> >> I think the grep()-family (regular expressions) will be the easiest
>> >> way to do this, though it sounds like you might prefer grepl() which
>> >> returns a logical vector:
>> >>
>> >> ^[AB] # Starts with either an A or a B
>> >> ^A_ # Starting with A_
>> >>
>> >> a <- c("A_A","A_B","C_A","BB","A_Asd"
>> >> grepl("^[AB]", a)
>> >> grepl("^A_")
>> >
>> > Yes grepl() is what I am looking for.
>> > is there also something like an OR statement e.g. if I want to
>> > select for elements that start with "as" OR "df"?
>>
>> > a <- c("as1", "bb", "as2", "cc", "df", "aa", "dd", "sdf")
>> > grepl("^as|^df", a)
>> [1] TRUE FALSE TRUE FALSE TRUE FALSE FALSE FALSE
>>
>>
>> The square brackets match any of those characters, so are good
>> for single characters. For more complex patterns, | is the or symbol.
>> ^ marks the beginning.
>
> Thank you so much Sarah! I tried that | symbol intuitively, there was just a
> problem with the quotation marks :(
>
> Now everything is solved...
>
> /johannes
>
>>
>> Sarah
>>
>> --
>> Sarah Goslee
>> http://www.functionaldiversity.org
>
> --
>
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> and provide commented, minimal, self-contained, reproducible code.
--
Gregory (Greg) L. Snow Ph.D.
[email protected]
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