R help - Jul 2010 - Deleting a variable number of characters from a string

I have a text processing problem I'm hoping someone can help me solve.  This
issue it this.

 I have a character string in which I need to delete a variable number of
characters from the string.  The string itself contains the number of characters
to be deleted.  The number of characters to be deleted is proceeded by either a
"+" or a "-".

A toy example:

Suppose I have

x<-c("A-1CB-2GHX",
"*+11gAgggTgtgggH")
> x
[1] "A-1CB-2GHX"       "*+11gAgggTgtgggH"

What I need as output is
"ABX" "*H"

I know I can use gsub to remove the control character and the number portion
with

gsub("(\\-|\\+)([0-9]+)", replacement="", x)

However, I can't figure out how to delete the variable number of characters
after the number portion of the string.

Any ideas?


In case this helps
> sessionInfo()
R version 2.11.1 (2010-05-31)
x86_64-pc-mingw32

locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252

Brian

	[[alternative HTML version deleted]]

Hi Davis, 

Please try ??regex

gsub("(\\-|\\+)([0-9]+)(\\w*)(\\w)", replacement="\\4", x)

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On Fri, Jul 16, 2010 at 1:59 PM, Davis, Brian <Brian.Davis at uth.tmc.edu>
wrote:
> I have a text processing problem I'm hoping someone can help me solve.
?This issue it this.
>
> ?I have a character string in which I need to delete a variable number of
characters from the string. ?The string itself contains the number of characters
to be deleted. ?The number of characters to be deleted is proceeded by either a
"+" or a "-".
>
> A toy example:
>
> Suppose I have
>
> x<-c("A-1CB-2GHX", "*+11gAgggTgtgggH")
>> x
> [1] "A-1CB-2GHX" ? ? ? "*+11gAgggTgtgggH"
>
> What I need as output is
> "ABX" "*H"
>
> I know I can use gsub to remove the control character and the number
portion with
>
> gsub("(\\-|\\+)([0-9]+)", replacement="", x)
>
> However, I can't figure out how to delete the variable number of
characters after the number portion of the string.
>
Using gsubfn in the gsubfn package we match

- the - or + via [-+],
- the digits via \\d+ and
- the remaining characters via [^-+]*

parenthesizing the digits and remaining characters so that they form
back references which are passed to the function as args 1 and 2
respectively.  gsubfn supports a formula notation for functions and the
specified function using that formula notation has arguments d and s
and function body which strips the characters and returns the rest
to be substituted back in:

   > library(gsubfn)
   > gsubfn("[-+](\\d+)([^-+]*)", d + s ~ substring(s,
as.numeric(d) + 1), x)
   [1] "ABX" "*H"

See http://gsubfn.googlecode.com for more.