# [R] simplify loop

Achim Zeileis Achim.Zeileis at wu-wien.ac.at
Wed May 11 19:21:13 CEST 2005

```On Wed, 11 May 2005 13:05:58 -0400 Omar Lakkis wrote:

> Is there a way to implement this faster than doing it in a loop.
>
>         for (i in length(settle)-1:1) {
>                 settle[i] = settle[i+1]/(1 + settle.pct[i+1])
>         }
>
> I want to guarantee that i+1 is calculated before i

Yes, as the loop above as only one iteration, you can easily do it as:
n <- length(settle)
settle[n-1] <- settle[n]/(1 + settle.pct[n])

What you probably really meant, can also be simply done without a for
loop. You need a vector settle.pct and a scalar starting value (not a
full vector) settle. So in the following settle is assumed to be only
settle[n]:

settle/c(rev(cumprod(1 + rev(settle.pct)))[-1], 1)

If settle.pct should in fact also be only be constant, this can of
course be further simplified.
Z

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