R help - Apr 2011 - regular expression for nth character in a string

Hi, I have a string

"InTrouble"

and want to extract, say, the first two characters: "In"
or the last three: "blee"
or the 3rd, 4th, and 5th: "Trou"

Is there an easy way of doing this quickly with regular expressions in gsub,
grep or similar?

Thank you for any help.

Gon?alo

On 04/25/2011 08:17 PM, Gon?alo Ferraz wrote:
> Hi, I have a string
>
> "InTrouble"
>
> and want to extract, say, the first two characters: "In"
> or the last three: "blee"
> or the 3rd, 4th, and 5th: "Trou"
>
> Is there an easy way of doing this quickly with regular expressions in
gsub, grep or similar?
>
Hi Gon?alo,
You could always try:

Im<-"InTrouble"
paste(unlist(strsplit(Im,""))[c(7,4,1,2,9,8,5,6,3)],collapse="")

Jim

will this do it:

> x <- "InTrouble"
> sub("^(..).*", "\\1", x)  # first two
[1] "In"
> sub(".*(...)$", "\\1", x)  # last three
[1] "ble"
> sub("^..(...).*", "\\1", x)  # 3rd,4th,5th char
[1] "Tro"
>

2011/4/25 Gon?alo Ferraz <gferraz29 at gmail.com>:
> Hi, I have a string
>
> "InTrouble"
>
> and want to extract, say, the first two characters: "In"
> or the last three: "blee"
> or the 3rd, 4th, and 5th: "Trou"
>
> Is there an easy way of doing this quickly with regular expressions in
gsub, grep or similar?
>
> Thank you for any help.
>
> Gon?alo
>
> ______________________________________________
> 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
Data Munger Guru

What is the problem that you are trying to solve?

On Apr 25, 2011, at 6:17 AM, Gon?alo Ferraz wrote:
> Hi, I have a string
>
> "InTrouble"
>
> and want to extract, say, the first two characters: "In"
> or the last three: "blee"
> or the 3rd, 4th, and 5th: "Trou"
>
> Is there an easy way of doing this quickly with regular expressions  
> in gsub, grep or similar?

Not greppish but seems to be the obvious approach:

 > substr("Trouble", 1,2)
[1] "Tr"
 > substr("Trouble", 3,5)
[1] "oub"

The greppish ways:

 > sub("(^..)(.*$)", "\\1", "Troubles")
[1] "Tr"

 > sub("(^..)(...)(.*$)", "\\2", "Troubles")
[1] "oub"
 > sub("(^..)(.{3})(.*$)", "\\2", "Troubles")
[1] "oub"

-- 

David Winsemius, MD
West Hartford, CT

2011/4/25 Gon?alo Ferraz <gferraz29 at gmail.com>:
> Hi, I have a string
>
> "InTrouble"
>
> and want to extract, say, the first two characters: "In"
> or the last three: "blee"
> or the 3rd, 4th, and 5th: "Trou"
>
> Is there an easy way of doing this quickly with regular expressions in
gsub, grep or similar?
>
strapply in gsubfn can readily do that.  It returns the matched part
or, if parentheses are used, only the part in parentheses:
> library(gsubfn)
> strapply("InTrouble", "^..", simplify = TRUE)
[1] "In"
> strapply("InTrouble", "...$", simplify = TRUE)
[1] "ble"
> strapply("InTrouble", "^..(...)", simplify = TRUE)
[1] "Tro"
> strapply("InTrouble", "^.{2}(.{3})", simplify = TRUE)
[1] "Tro"


-- 
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GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
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