[R] Retain last grouping after a strsplit()

[Steven Ranney]

David and Jim -

Thanks for your help.  Your suggestions worked just fine.  Now my task
is to learn why the random-looking string of characters in the first
part of Jim's sub() statement aren't really so random.

Thanks again -

SR
Steven H. Ranney


On Tue, Dec 11, 2012 at 11:37 AM, David Winsemius
<dwinsemius at comcast.net> wrote:
>
> On Dec 11, 2012, at 10:10 AM, jim holtman wrote:
>
>> try this:
>>
>>> x
>>
>> [1] "OYS-PIA2-FL-1"  "OYS-PIA2-LA-1"  "OYS-PI-LA-BB-1" "OYS-PIA2-LA-10"
>>>
>>> sub("^.*?([0-9]+)$", "\\1", x)
>>
>> [1] "1"  "1"  "1"  "10"
>>>
>>>
>>
>>
>
> Steve;
>
> jim holtman is one of the jewels of the rhelp world. I generally assume that
> his answers are going to be the most succinct and efficient ones possible
> and avoid adding noise, but here I thought I would try to improve. Thinking
> there might be a string-splitting approach I first tried (and discovered a
> not-so-great solution:
>
>  x <- c("OYS-PIA2-FL-1",  "OYS-PIA2-LA-1",  "OYS-PI-LA-BB-1",
> "OYS-PIA2-LA-10")
>  sapply( strsplit(x, "-") , "[", 4)
> [1] "1"  "1"  "BB" "10"
>
> So then I asked myself if we could just "blank out" everything before the
> last das, finding what seemed to be a fairly economical solution and one
> that does not require back-references:
>
>  sub( "^.+-" , "", x)
>
> [1] "1"  "1"  "1"  "10"
>
> If there were no digits after the last dash these approaches give different
> results:
>
>  x <- c("OYS-PIA2-FL-1",  "OYS-PIA2-LA-1",  "OYS-PI-LA-BB-1",
> "OYS-PIA2-LA-")
>
>  sub( "^.+-" , "", x)
>
> [1] "1" "1" "1" ""
>
>  sub("^.*?([0-9]+)$", "\\1", x)
> [1] "1"            "1"            "1"            "OYS-PIA2-LA-"
>
> When a grep pattern does not match, sub and gsub will return the whole
> argument.
>
> --
> David.
>
>>
>> On Tue, Dec 11, 2012 at 12:46 PM, Steven Ranney <steven.ranney at gmail.com>
>> wrote:
>>>
>>> OYS-PIA2-FL-1
>>> OYS-PIA2-LA-1
>>> OYS-PI-LA-BB-1
>>> OYS-PIA2-LA-10
>>
>>
>>
>>
>> --
>> Jim Holtman
>> Data Munger Guru
>>
>> What is the problem that you are trying to solve?
>> Tell me what you want to do, not how you want to do it.
>>
>> ______________________________________________
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>> and provide commented, minimal, self-contained, reproducible code.
>
>
> David Winsemius, MD
> Alameda, CA, USA
>