Re: [R] avoiding a loop

From: Christos Hatzis <>
Date: Tue 24 Oct 2006 - 19:00:33 GMT

Try this (essentially the trick is to shift the invector to get the y[i-i] effect):

constructLt<-function(invector, a=1) {

    invector[invector<a] <- c(0,invector)[invector<a] * invector[invector<a]     invector

> aa <- c(1,1,0.5,2,3,0.4,4,5)
> aa

[1] 1.0 1.0 0.5 2.0 3.0 0.4 4.0 5.0
> constructLt(aa)

[1] 1.0 1.0 0.5 2.0 3.0 1.2 4.0 5.0


-----Original Message-----
[] On Behalf Of Leeds, Mark (IED) Sent: Tuesday, October 24, 2006 2:36 PM
Subject: [R] avoiding a loop

I think I asked a similar question 3 years ago to the Splus list and I think the answer was no or noone answered so noone should spend more than 5 minutes on this because it could definitely be a waste of time.  

My question is whether the function below can be rewritten without a for loop. apply is fine if it can be done that way but i doubt it. I call it a lot and would prefer to not loop.  


constructLt<-function(invector) {  


 for ( i in 2:length(invector) ) {
 if ( invector[i] < 1 ) {
  outvector[i]<-invector[i]*outvector[i-1]  }




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