[R] question to make a vector without loop

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of 
> khazaei at ceremade.dauphine.fr
> Sent: Friday, February 26, 2010 7:23 AM
> To: r-help at r-project.org
> Subject: [R] question to make a vector without loop
> 
> Hello all,
> 
> I want to define a vector like w[k+1]=w[k]*a/(b+k) for 
> k=1,...,N-1 without
> use loop. Is it posible to do in R?

It would be nice to see your loopy solution.
However, you could use cumprod (cumulative
products):
   c(w[1], w[1] * cumprod(a/(b+seq_len(N-1)))
E.g.,
   > w<-7
   > a<-2
   > b<-1
   > for(k in 1:9) w[k+1] <- w[k] * a / (b+k)
   > w
    [1] 7.0000000000 7.0000000000 4.6666666667 2.3333333333 0.9333333333
    [6] 0.3111111111 0.0888888889 0.0222222222 0.0049382716 0.0009876543
   > c(w[1], w[1]*cumprod(a/(b+seq_len(9))))
    [1] 7.0000000000 7.0000000000 4.6666666667 2.3333333333 0.9333333333
    [6] 0.3111111111 0.0888888889 0.0222222222 0.0049382716 0.0009876543

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  

> 
> Regards
> 
> khazaei
> 
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