[R] Simple - Finding vector in a vector

[Mike Spam]

Hi,

just a simple question.
Assumed i have a vector,

FALSE  TRUE  TRUE  TRUE FALSE  TRUE FALSE  TRUE FALSE
or
NA  1  1  1 NA  1 NA  1 NA

what i need is the position where an element is the same - three (or
in general multiple) times in a row.

in this case: i want to get the position where it is TRUE TRUE TRUE or 1 1 1
it doesn't matter if it is the first, middle or last element. So the
output could be 2 or 3 or 4

My idea would be to lag the vector and calc differences... but i would
prefer any build in (or time saving) function. :)

thanks,

Nico