[R] R Regular Expressions - Metacharacters

[David Winsemius]

On Feb 5, 2013, at 9:49 AM, Seth Dickey wrote:

> I thought that I can use metacharacters such as \w to match word characters
> with one backslash.  But for some reason, I need to include two backslashes.
> 
>> grepl(pattern='\w', x="what")
> Error: '\w' is an unrecognized escape in character string starting "\w"
> 
>> grepl(pattern='\\w', x="what")
> [1] TRUE
> 
> I can't find the reason for this on the help pages.  Does anyone know why?

The help page for ?regex says near the top ...

"Any metacharacter with special meaning may be quoted by preceding it with a backslash. The metacharacters in EREs are . \ | ( ) [ { ^ $ * + ?, but note that whether these have a special meaning depends on the context."
> 
> Thanks!
> 
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> 
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David Winsemius
Alameda, CA, USA