[R] counts of a vector

[William Dunlap]

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of speretti
> Sent: Wednesday, May 26, 2010 10:22 AM
> To: r-help at r-project.org
> Subject: [R] counts of a vector
> 
> 
> Hi,
> 
> I need help to find an efficient way to transform a vector like:
> 
> a<-c(1,1,0,1,0,0,0,1,1,1,1,0,1,0,1,1)
> 
> in a vector that counts only di 1 elements, like:
> 
> b<-c(1,2,0,1,0,0,0,1,2,3,4,0,1,0,1,2)

The following is pretty quick:

  > f <-  function (x) {
      # x must be entirely composed of 0's and 1's or FALSE's and
TRUE's.
      csx <- cumsum(x)
      csx - cummax(csx * (1-x)) # 1-x could also be !x
  }
  > all.equal(f(a), b)
  [1] TRUE
 
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> 
> 
> Thank you!
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