[S] Looping

[Lars Karlsson <lars@ana.unibe.ch>]

Is there a way to avoid the loops below?
vec is a vector of length n. I want to count the number of instances
where an element and the next j-th element both equals 1.

n <- length (vec)
aaa <- rep (0, n)
for (j in 0:(n-1)){
   aa <- 0
   for (i in 1:(n - j)){
      if ( vec[i] == 1 & vec[i+j] == 1 ) aa <- aa + 1
   }
   aaa[j+1] <- aa
}

For example:
> vec <- c(1,0,1,1,2,1,2,1,0,1)
yields
> aaa
 [1] 6 1 4 2 2 2 1 2 0 1


Thanks in advance for any help.
/Lars

----------------------------------------------------------
 Tekn.Dr. Lars M. Karlsson     Tel:   +41 (0)31 631 84 52 
 Department of Anatomy         Fax:   +41 (0)31 631 34 10 
 University of Berne           mailto:Lars@ana.unibe.ch   
 Buelstrasse 26                   
 CH-3000 Berne 9                                          
 Switzerland
 http://www.ana.unibe.ch/ANATOM/staff/karlsson/index.html
                           
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