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

[Jeff Newmiller]

So what is the special behavior of the ^ symbol when not at the beginning of the string that occurs when it is not escaped?
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Duncan Murdoch <murdoch.duncan at gmail.com> wrote:

>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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>> Jeff Newmiller                        The     .....       .....  Go
>Live...
>> DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
>Go...
>>                                        Live:   OO#.. Dead: OO#.. 
>Playing
>> Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
>> /Software/Embedded Controllers)               .OO#.       .OO#. 
>rocks...1k
>>
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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.
>>