# [R] dependent nested for loops in R

Shaami nz@h@@m @end|ng |rom gm@||@com
Sun Jan 31 06:32:02 CET 2021

```Hi
I have made the sample code again. Could you please guide how to use
vectorization for variables whose next value depends on the previous one?

w = NULL

for(j in 1:1000)

{

z = NULL

x = rnorm(2000)

z[1] = x[1]

for(i in 2:2000)

{

z[i] = x[i]+5*z[i-1]

if(z[i]>4 | z[i]<1) {

w[j]=i

} else {

w[j] = 0

}

}

}

On Sun, Jan 31, 2021 at 10:01 AM David Winsemius <dwinsemius using comcast.net>
wrote:

>
> On 1/30/21 8:26 PM, Shaami wrote:
> > Hi
> > I have very large dependent nested for loops that are quite expensive
> > computationally. It takes weeks and does not end to give me results.
> Could
> > anyone please guide how could I use apply function or any other
> suggestion
> > for such big and dependent loops in R? A sample code is as follows.
> >
> > w = NULL
> > for(j in 1:1000)
> > {
> >    x = rnorm(2000)
> >    z = x[1]
> >    for(i in 2:2000)
> >    {
> >      z = x[i]+5*z[i-1]
>
> I'm guessing you meant to type:
>
>          z[i] <- x[i]+5*z[i-1]
>
> >      if(z>4 | z<1) {
>
> And more guesses (in the absence of any sort of problem description)
> that you really wanted:
>
>
>   if(z[i]>4 | z[i]<1) {  ....
>
>
> >        w[j]=i
> >        break
> >      } else {
> >        w[j] = 0
> >      }
> >    }
> > }
>
>
> Are you sure you need a for-loop? Seems like you could have done this
> with a couple of vectorized operations. And the `break` looked entirely
> superfluous.
>
>
>
> > Thank you
> >
> >       [[alternative HTML version deleted]]
> >
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