dependent nested for loops in R

On 1/31/21 1:26 PM, Berry, Charles wrote:

On Jan 30, 2021, at 9:32 PM, Shaami <nzshaam at gmail.com> wrote:

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?

I agree with Charles that I suspect your results are not what you
expect. You should try using cat or print to output intermediate results
to the console. I would suggest you limit your examination to a more
manageable length, say the first 10 results while you are working out
your logic. After you have the logic debugged, you can move on to long
sequences.


This is my suggestion for a more compact solution (at least for the
inner loop calculation):

set.seed(123)

x <- rnorm(2000)

z <- Reduce( function(x,y) { sum(y+5*x) }, x, accumulate=TRUE)

w<- numeric(2000)

w <-  (1:2000)[ z >4 | z < 1 ]  # In your version the w values get
overwritten and end up all being 2000


I would also advise making a natural language statement of the problem
and goals. I'm thinking that you may be missing certain aspects of the
underying problem.

--

David.

Glad to help.

First, it could help you to trace your code.  I suspect that the results

are not at all what you want and tracing would help you see that.

I suggest running this revision and printing out x, z, and w.

#+begin_src R
   w = NULL
   for(j in 1:2)
   {
     z = NULL
     x = rnorm(10)
     z[1] = x[1]
     for(i in 2:10)
     {
       z[i] = x[i]+5*z[i-1]
       if(z[i]>4 | z[i]<1) {
      w[j]=i
       } else {
      w[j] = 0
       }
     }
   }
#+end_src


You should be able to see that the value of w can easily be obtained

outside of the `i' loop.