[R] About grep
Hi,everyone.
I have a problem when using the grep.
for example:
a <- c("aa","aba","abac")
b<- c("ab","aba")
I want to match the whole word,so
grep("^aba$",a)
it returns 2
but when I used it a more useful way:
grep("^b[2]$",a),
it doesn't work at all, it can't find it, returning integer(0).
How can I chang the format in the second way?
Thanks.
--
Shao
[[alternative HTML version deleted]]
__
R-help@stat.math.ethz.ch 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.
Re: [R] About grep
try
grep(paste("^",b[2],"$",sep=""),a)
your version will match "b2":
> grep("^b[2]$",c("b","b2","b3"))
[1] 2
--- Shao <[EMAIL PROTECTED]> wrote:
> Hi,everyone.
>
> I have a problem when using the grep.
> for example:
> a <- c("aa","aba","abac")
> b<- c("ab","aba")
>
> I want to match the whole word,so
> grep("^aba$",a)
> it returns 2
>
> but when I used it a more useful way:
> grep("^b[2]$",a),
> it doesn't work at all, it can't find it, returning integer(0).
>
> How can I chang the format in the second way?
>
> Thanks.
>
> --
> Shao
>
> [[alternative HTML version deleted]]
>
> __
> R-help@stat.math.ethz.ch 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.
>
Pinpoint customers who are looking for what you sell.
__
R-help@stat.math.ethz.ch 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.
Re: [R] About grep
Oh,great.
Thanks.
On 8/7/07, Stephen Tucker <[EMAIL PROTECTED]> wrote:
>
> try
>
> grep(paste("^",b[2],"$",sep=""),a)
>
>
> your version will match "b2":
>
> > grep("^b[2]$",c("b","b2","b3"))
> [1] 2
>
>
> --- Shao <[EMAIL PROTECTED]> wrote:
>
> > Hi,everyone.
> >
> > I have a problem when using the grep.
> > for example:
> > a <- c("aa","aba","abac")
> > b<- c("ab","aba")
> >
> > I want to match the whole word,so
> > grep("^aba$",a)
> > it returns 2
> >
> > but when I used it a more useful way:
> > grep("^b[2]$",a),
> > it doesn't work at all, it can't find it, returning integer(0).
> >
> > How can I chang the format in the second way?
> >
> > Thanks.
> >
> > --
> > Shao
> >
> > [[alternative HTML version deleted]]
> >
> > __
> > R-help@stat.math.ethz.ch 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.
> >
>
>
>
>
>
>
> Pinpoint customers who are looking for what you sell.
> http://searchmarketing.yahoo.com/
>
--
Shao
[[alternative HTML version deleted]]
__
R-help@stat.math.ethz.ch 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.
Re: [R] About grep
Shao wrote:
>
> Hi,everyone.
>
> I have a problem when using the grep.
> for example:
> a <- c("aa","aba","abac")
> b<- c("ab","aba")
>
> I want to match the whole word,so
> grep("^aba$",a)
> it returns 2
>
> but when I used it a more useful way:
> grep("^b[2]$",a),
> it doesn't work at all, it can't find it, returning integer(0).
>
> How can I chang the format in the second way?
>
> Thanks.
>
The regexp "^b[2]$" matches only two words: "b2" and "b" (in your present
grep call with defaults
extended = TRUE, perl = FALSE, fixed = FALSE).
They don't present in a, that's why grep returns integer(0).
If you want to find the word "b[2]" (the expression similar to an array
indexing operator), either use fixed=TRUE and remove any regexp markup (^
and $)
> a<- c("aa","aba","abac","b[2]")
> grep("b[2]",a,fixed=TRUE)
[1] 4
, or use escapes
> grep("^b\\[2\\]$",a)
[1] 4
--
View this message in context:
http://www.nabble.com/About-grep-tf4228021.html#a12029243
Sent from the R help mailing list archive at Nabble.com.
__
R-help@stat.math.ethz.ch 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.
Re: [R] About grep
On 07-Aug-07 04:20:27, Shao wrote:
> Hi,everyone.
>
> I have a problem when using the grep.
> for example:
> a <- c("aa","aba","abac")
> b<- c("ab","aba")
>
> I want to match the whole word,so
> grep("^aba$",a)
> it returns 2
>
> but when I used it a more useful way:
> grep("^b[2]$",a),
> it doesn't work at all, it can't find it, returning integer(0).
>
> How can I chang the format in the second way?
>
> Thanks.
>
> --
> Shao
The problem is that in the string "^b[2]$" the element b[2] of b
is not evaluated, but simply the successive characters ^ b [ 2 ] $
are passed to grep as a character string, which of course is not
found. You can construct a character string with the value of b[2]
in it by using paste():
grep(paste("^",b[2],"$",sep=""),a)
[1] 2
Ted.
E-Mail: (Ted Harding) <[EMAIL PROTECTED]>
Fax-to-email: +44 (0)870 094 0861
Date: 07-Aug-07 Time: 07:43:14
-- XFMail --
__
R-help@stat.math.ethz.ch 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.
