R help - Jan 2021 - dependent nested for loops in R

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]
    if(z>4 | z<1) {
      w[j]=i
      break
    } else {
      w[j] = 0
    }
  }
}


Thank you

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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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