On Jul 7, 2011, at 11:21 AM, Bogaso Christofer wrote:
> Hi there, I have to extract some relevant portion from a defined string,
> which is a mix of numeric and character. However this has following
> sequence:
>
>
>
> Some String - Some numerical - "c/C" (or "p/P") - then
again some set of
> numbers.
>
>
>
> Examples of such string is "fdahsdfcha163517253c463278643" or
> "fdahsdfcha163517253C463278643" or
"fdahsdfcha163517253P463278643",
> "fdahsdfcha163517253p463278643" etc.
>
>
>
> I have tried using latest stringr package to accomplice that. Here is my
> try:
>
>
>
>> library(stringr)
>
>> str_extract("fdahsdfcha163517253c463278643", "[c]")
>
> [1] "c"
>
>
>
> But it seems that, above code fetching "c" from
"fdahsdfcha" only. My goal
> is to understand what is there between above 2 set of numbers,
"C/c/P/p"?
> Can somebody help me how to do that? I would like to use stringr syntax
> because, I am already using lot of other functions from that. Therefore if
I
> can do it using that package then it would be good in terms of consistency.
>
>
>
> Thanks for your help.
I don't use 'stringr', but you can get the desired result using
?gsub:
x <- c("fdahsdfcha163517253c463278643",
"fdahsdfcha163517253C463278643",
"fdahsdfcha163517253P463278643",
"fdahsdfcha163517253p463278643")
> gsub(".+[0-9]+([cCpP])[0-9]+", "\\1", x)
[1] "c" "C" "P" "p"
The regex in the first argument tells gsub to find a sequence of any characters,
followed by a sequence of numbers, followed a by single 'c',
'C', 'p' or 'P', finally followed by a sequence of
numbers.
Surrounding the [cCpP] in parens allows us to use a 'back reference' and
return what is found within the parens using the "\\1" in the second
argument.
>From a brief review of the stringr manual, it looks like str_extract()
supports the use of a regex for the pattern argument, but does not support the
use of back references. It looks like str_replace_all() is a wrapper to gsub(),
so you may want to look at that function and the examples for it. Thus, the
syntax might be something like:
str_replace_all(x, ".+[0-9]+([cCpP])[0-9]+", "\\1")
and therefore, I am not sure what you are really saving by using it versus
gsub() directly.
HTH,
Marc Schwartz