[R] replace a whole word with sub()

[Marc Schwartz]

On Nov 13, 2009, at 9:13 AM, Giulio Di Giovanni wrote:

>
>
>
> Dear all,
>
>
>
> I cannot figure out how to solve a small problem (well, not for me),  
> surely somebody can help me in few seconds.
>
>
>
> I have a series of strings in a vector X of the type  "xxx", "yyy",  
> "zzz", "IgA", "IgG", "kkk", "IgM", "aaa".
>
> I want to substitute every ENTIRE string beginning with "Ig" with "0".
>
> So, I'd like to have "xxx", "yyy", "zzz", "0", "0", "kkk", "0", "aaa".
>
>
>
> I can easily identify these strings with grep("^Ig", X), but if I  
> use this criterion in the sub() function (sub("^Ig", "0", X) I  
> obviously get "0A", "0G" etc.
>
>
>
> I didn't expect to do it in this way and I tried with metacharacters  
> and regexps in order to grep and substitute the whole word (\b \>,  
> $). I don't post here my tryings,  because they were obviously wrong.
>
> Please can you help me?


x <- c("xxx", "yyy", "zzz", "IgA", "IgG", "kkk", "IgM", "aaa")

 > sub("^Ig.*$", "0", x)
[1] "xxx" "yyy" "zzz" "0"   "0"   "kkk" "0"   "aaa"

You need to have the search regex include the entire element and not  
just the first couple of characters in order to replace the entire  
element.

HTH,

Marc Schwartz