R help - Dec 2009 - how to count the total number of (INCLUDING overlapping) occurrences of a substring within a string?

Last one for you guys:

The command:

length(gregexpr('cus','hocus pocus')[[1]])
[1] 2

returns the number of times the substring 'cus' appears in 'hocus
pocus'
(which is two)

It's returning the number of **disjoint** matches.  So:

length(gregexpr('aa','aaa')[[1]])
 [1] 1

returns 1.

**What I want to do:**
I'm looking for a way to count all occurrences of the substring, including
overlapping sets (so 'aa' would be found in 'aaa' two times,
because the
middle 'a' gets counted twice).

Any ideas would be much appreciated!!

Signing off and thanks for all the great assistance,
Jonathan

	[[alternative HTML version deleted]]

Use a zero lookaround expression.  It will not consume its match.  See ?regexp
> gregexpr("a(?=a)", "aaa", perl = TRUE)
[[1]]
[1] 1 2
attr(,"match.length")
[1] 1 1


On Sun, Dec 20, 2009 at 1:43 AM, Jonathan <jonsleepy at gmail.com>
wrote:
> Last one for you guys:
>
> The command:
>
> length(gregexpr('cus','hocus pocus')[[1]])
> [1] 2
>
> returns the number of times the substring 'cus' appears in
'hocus pocus'
> (which is two)
>
> It's returning the number of **disjoint** matches. ?So:
>
> length(gregexpr('aa','aaa')[[1]])
> ?[1] 1
>
> returns 1.
>
> **What I want to do:**
> I'm looking for a way to count all occurrences of the substring,
including
> overlapping sets (so 'aa' would be found in 'aaa' two
times, because the
> middle 'a' gets counted twice).
>
> Any ideas would be much appreciated!!
>
> Signing off and thanks for all the great assistance,
> Jonathan