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nested do loop with iml

Super Contributor
Posts: 345

nested do loop with iml

I need to write a funtion or module that creates a row vector called doit of dimmesion k(k-1)/2 that contains the pairwise differences between the k leverl means. I need nested do loops

doit[i,j]= Yi0 hat- Yjo hat


below is my code

a=3;   # k level  (maybe I can replace it with ncol (mymatrix)?)


do i= 1 to a;

do j = i to a;

dime = group_mean[i]-groupmean[j];

doit= doit||dime;



but it does not work. ANy other suggestions to make it work? Any other solutions

Regular Contributor
Posts: 163

Re: nested do loop with iml

I am not sure what you mean by the line of code that starts doit[i,j]=...   however the code below that can be made to work.  The problems are:

  • the do loops allow i to be equal to j - you probably do not want the zeros that will result from this.
  • either group_mean or groupmean is a typo.

If you still cannot make it work, then please show us the messages that you are getting in the log.


In general it is a bad habit to grow matrices by concatenation inside a loop - this is very inefficient in terms of memory use.  For a=3 you will probably not notice, but similar code with a=1000 would grind to a halt.

Posts: 4,176

Re: nested do loop with iml

Posted in reply to IanWakeling

For a more on Ian's comment about concatenating inside a DO loop (as well as an alternative approach), see the article "Friends don't let friends concatenate results inside a loop."

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