Thanks for your reply, though this still wouldn't work with a function for example, starting code like below fails because x is read as a vector as opposed to doing it for x=1 then x=2 - is there any way of tweaking the code easily, or do I just resign myself to for loops to do that?
   
  x<-1:4
  trial<- function(x)
  {xx<-matrix(runif(20), 2, 10)
  if (xx[1,x]<0.5) { ...}
   
  Thanks
   
  Paul
  

Jacques VESLOT <jacques.veslot@good.ibl.fr> wrote:
  ?cumsum

> system.time({ z <- NULL ; for (i in 1:1000) z <- c(z, sum((1:i)**2)) })
[1] 0.04 0.00 0.04 NA NA
> system.time( zz <- cumsum((1:1000)**2) )
[1] 0 0 0 NA NA
> all.equal(z,zz)
[1] TRUE

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Paul Chatfield a écrit :
> Hi - I'm trying to avoid using a 'for' loop due to inefficiency and instead use a function (and ultimately tapply as I'm working on a matrix) but I can't figure out how to get 'function' to take the variables as anything other than vectors for example
> 
> aa<-0
> x<-1:4
> test.fun<-function(x)
> {aa<-(x*x +aa) 
> return(aa)}
> test.fun(1:4)
> 
> This code returns 'aa' as 1 4 9 16, but I'd like it to return aa as 1 5 14 30 taking into consideration that I've just calculated aa for x=1. Aside from using loops, is there not a simple way of telling R to work out x for consecutive values?
> 
> thanks
> 
> Paul Chatfield
> 
> 

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