[R] Regex for ^ (the caret symbol)?

[Jeff Newmiller]

I am not sure I understand what worked perfectly, since it is my understanding that ^ is only special at the beginning of the regex (to anchor the pattern at the beginning of the target string) or as the first character of a character set (to indicate exclusion of the listed characters). In any other position the caret should behave like an ordinary character. That is, your original pattern should have worked as-is. This is supported by the help page documentation for regex in the paragraph below the definition of [:xdigit:]. I think this is a bug in R.

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mtb954 at gmail.com wrote:

>Hi Tsjerk, many thanks...that worked perfectly!
>
>Mark Na
>
>
>
>On Mon, Jan 21, 2013 at 9:36 AM, Tsjerk Wassenaar <tsjerkw at gmail.com>
>wrote:
>
>> Oh, I'm jetlagged. ^ is a control character for 'start of string'. In
>the
>> context of a character set it means negation: [^a-z].
>>
>> Ciao,
>>
>> Tsjerk
>>
>>
>> On Mon, Jan 21, 2013 at 4:33 PM, Tsjerk Wassenaar
><tsjerkw at gmail.com>wrote:
>>
>>> Hi Mark Na,
>>>
>>> Try:
>>>
>>> grepl("latitude\\^2",temp)
>>>
>>> ^ is a control character for negation, so you have to escape it.
>>>
>>> Cheers,
>>>
>>> Tsjerk
>>>
>>>
>>> On Mon, Jan 21, 2013 at 4:26 PM, <mtb954 at gmail.com> wrote:
>>>
>>>> Hello R-helpers,
>>>>
>>>> I am trying to search for string that includes the caret symbol,
>using
>>>> the
>>>> following code:
>>>>
>>>> grepl("latitude^2",temp)
>>>>
>>>>
>>>> And R doesn't like that. It gives me:
>>>>
>>>> > temp<-c("latitude^2","latitude and
>latitude^2","longitude^2","longitude
>>>> and longitude^2")
>>>> > temp
>>>> [1] "latitude^2"                "latitude and latitude^2"  
>"longitude^2"
>>>>             "longitude and longitude^2"
>>>> > grepl("latitude^2",temp)
>>>> [1] FALSE FALSE FALSE FALSE
>>>>
>>>>
>>>> I think this must a regex problem, but I can't find out to specify
>the
>>>> caret using regex.
>>>>
>>>> I would appreciate any help you could provide.
>>>>
>>>> Many thanks,
>>>>
>>>> Mark Na
>>>>
>>>>         [[alternative HTML version deleted]]
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>
>>>
>>>
>>>
>>> --
>>> Tsjerk A. Wassenaar, Ph.D.
>>>
>>> post-doctoral researcher
>>> Biocomputing Group
>>> Department of Biological Sciences
>>> 2500 University Drive NW
>>> Calgary, AB T2N 1N4
>>> Canada
>>>
>>
>>
>>
>> --
>> Tsjerk A. Wassenaar, Ph.D.
>>
>> post-doctoral researcher
>> Biocomputing Group
>> Department of Biological Sciences
>> 2500 University Drive NW
>> Calgary, AB T2N 1N4
>> Canada
>>
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.