On Fri, Jul 16, 2010 at 1:59 PM, Davis, Brian <brian.da...@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.
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