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

[Duncan Murdoch]

On 13-01-21 11:48 AM, Jeff Newmiller wrote:
> 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.

It's a documentation error rather than a bug.  The ^ character is 
special anywhere in the extended RE syntax defined by the TRE library
or the Perl-compatible library that we use.  This is inconsistent with 
the POSIX standard, which might be what you were thinking of.

Duncan Murdoch



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> Sent from my phone. Please excuse my brevity.
>
> 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.
>
> ______________________________________________
> 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.
>