[R] Use of [:alnum:] or . in gsub() etc..

[Marc Schwartz]

on 01/16/2009 10:13 AM ppaarrkk wrote:
> 
> test = c ( "AAABBB", "CCC" )
> 
> 
> This works :
> 
> gsub ( "[A-Z]", "2", test )
> 
> 
> 
> None of these do :
> 
> gsub ( "[A-Z]", [:alnum:], test )
> gsub ( "[A-Z]", [[:alnum:]], test )
> gsub ( "[A-Z]", "[:alnum:]", test )
> gsub ( "[A-Z]", "[[:alnum:]]", test )
> gsub ( "[A-Z]", "^[:alnum:]$", test )
> 
> 
> 
> What am I doing wrong, please ?

The syntax ordering is off. You are in effect trying to replace the
characters A-Z with the character vector "[[:alnum:]]". Thus:

> gsub ("[A-Z]", "[[:alnum:]]",  test )
[1] "[[:alnum:]][[:alnum:]][[:alnum:]][[:alnum:]][[:alnum:]][[:alnum:]]"
[2] "[[:alnum:]][[:alnum:]][[:alnum:]]"


Recall the basic syntax for gsub() is:

  gsub(SearchPattern, ReplacementVector, Source)


What you want is:

> gsub ("[[:alnum:]]", "2" , test )
[1] "222222" "222"


HTH,

Marc Schwartz