nested do loop with iml

[Bal23]

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)?)

doit={};

do i= 1 to a;

do j = i to a;

dime = group_mean[i]-groupmean[j];

doit= doit||dime;

end;

end;

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

[IanWakeling]

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.

[Rick_SAS]

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."