[R] pattern matching

[Marc Schwartz]

On Jan 7, 2013, at 3:22 PM, Data Analytics Corp. <walt at dataanalyticscorp.com> wrote:

> Hi,
> 
> I have a simple question.  Suppose I have a string "x$Expensive". I want to find the position of the $ in this string; i.e., I want a function that returns 2.  I tried grep, regexpr, etc with no luck, unless I'm just using them incorrectly.  Any suggestions?
> 
> Thanks,
> 
> Walt



The problem with this specific example is that '$' is a metacharacter in regular expressions, so you have to escape it. For example:

> regexpr("\\$", "x$Expensive")
[1] 2
attr(,"match.length")
[1] 1
attr(,"useBytes")
[1] TRUE



See ?regex for more information and if appropriate, consider gregexpr():

> gregexpr("\\$", "x$Expensive$MoreText")
[[1]]
[1]  2 12
attr(,"match.length")
[1] 1 1
attr(,"useBytes")
[1] TRUE


Regards,

Marc Schwartz