topic Re: nested do loop with iml in SAS/IML Software and Matrix Computations

nested do loop with iml

Bal23 — Fri, 10 Jun 2016 20:57:36 GMT

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;

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

Re: nested do loop with iml

IanWakeling — Sat, 11 Jun 2016 07:39:09 GMT

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.

Re: nested do loop with iml

Rick_SAS — Sat, 11 Jun 2016 11:56:07 GMT

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."