[R] problem with pattern matching

[Rnewbie]

Thank you very much for the answer. I just solved the problem by writing a
loop for grep(), so that R runs through the ID list one by one. Probably it
is not the ideal method, but still I can now proceed to further work.



William Dunlap wrote:
> 
>> -----Original Message-----
>> From: r-help-bounces at r-project.org 
>> [mailto:r-help-bounces at r-project.org] On Behalf Of jim holtman
>> Sent: Wednesday, August 05, 2009 5:23 AM
>> To: Rnewbie
>> Cc: r-help at r-project.org
>> Subject: Re: [R] problem with pattern matching
>> 
>> I think you want to use either 'match' or '%in%'
>> 
>> x <- dataframe$ID %in% list$ID  # TRUE if it is in list
> 
> grep(pattern,text) expects that pattern is a scalar string.
> It, like quite a few other R functions, will not alert you if
> you pass it several strings: it silently ignores all but the
> first.  S+'s grep() will throw an errorg if length(pattern)!=0.
> E.g.,
> 
> RS> grep(pattern=c("a+", "b+"), c("cat","dog","bear"), value=TRUE)
> S+: Problem in regexpr(pattern, text): pattern should be a single
> character string, length is 2
> S+: Use traceback() to see the call stack
> R : [1] "cat"  "bear"
> 
> I think it would be better if this error were caught at runtime.
> R does catch the 0-length argument, but gives a pretty generic
> error message (perhaps to make translations easier):
> 
> RS> grep(pattern=character(), c("cat","dog","beet"))
> S+: Problem in regexpr(pattern, text): pattern should be a single
> character string, length is 0
> S+: Use traceback() to see the call stack
> R : Error in grep(pattern = character(), c("cat", "dog", "beet")) :
> R :   invalid argument
> 
> Bill Dunlap
> TIBCO Software Inc - Spotfire Division
> wdunlap tibco.com 
> 
>> 
>> On Wed, Aug 5, 2009 at 5:36 AM, Rnewbie<xuancj at yahoo.com> wrote:
>> >
>> > I wanted to extract my interested rows from a dataframe. I used:
>> >
>> > grep(list$ID, dataframe$ID, value=T) #list contains a list 
>> of my interested
>> > IDs
>> >
>> > I got one match in return, which is the very first ID in 
>> list. It seems the
>> > matching process just stopped, once the first match was found.
>> >
>> >
>> >
>> > David Winsemius wrote:
>> >>
>> >>
>> >> On Aug 4, 2009, at 11:16 AM, Rnewbie wrote:
>> >>
>> >>>
>> >>> dear all,
>> >>>
>> >>> I got a problem with pattern matching using grep. I 
>> extracted a list
>> >>> of
>> >>> characters from a data frame, and I tried to match this list of
>> >>> characters
>> >>> to a column from another data frame. In return, I got only one
>> >>> match, but
>> >>> there should be far more matches. Any ideas what has gone wrong?
>> >>
>> >> In general this falls into the category of  a request to "read my
>> >> mind". One, out of probably an infinite number, of ways to 
>> get such a
>> >> result is to use if()  when you needed ifelse().
>> >>
>> >>>
>> >>> Another question, if I also want to match the whole of 
>> the elements
>> >>> against
>> >>> the non-initial parts of the elements in another table. Which
>> >>> command should
>> >>> I use?
>> >>
>> >> Cannot even assign a semantic meaning to that one. What is 
>> are "non-
>> >> initial parts of the elements of another table"?
>> >>
>> >>
>> >> ******************************************************************
>> >>>  .... provide commented, minimal, self-contained, 
>> reproducible code.
>> >> ******************************************************************
>> >>>
>> >>> Thanks
>> >>
>> >> David Winsemius, MD
>> >> Heritage Laboratories
>> >> West Hartford, CT
>> >>
>> >> ______________________________________________
>> >> 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.
>> >>
>> >>
>> >
>> > --
>> > View this message in context: 
>> http://www.nabble.com/problem-with-pattern-matching-tp24810298
>> p24823683.html
>> > Sent from the R help mailing list archive at Nabble.com.
>> >
>> > ______________________________________________
>> > 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.
>> >
>> 
>> 
>> 
>> -- 
>> Jim Holtman
>> Cincinnati, OH
>> +1 513 646 9390
>> 
>> What is the problem that you are trying to solve?
>> 
>> ______________________________________________
>> 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.
> 
> 

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