I have data where where I've taken some measurements three times... twice in 
rapid succession so I could check test-retest reliability of a piece of 
equipment, and then a third measurement some time later.

Not I'd like to do an analysis where I have two scores... the first being 
the mean of the first two taken the same day, and the second being the one 
taken later.

I have a lot of other variables in the row, and I'd like to do the same 
thing to all of them. Soo....

Data.Frame:

Subj Obs MeasureA MeasureB
1 1 45 685
1 2 50 690
1 3 48 693
2 1 39 595
2 2 41 585
2 3 45 343

should become:
Subj Obs MeasureA MeasureB
1 1 47.5 687.5
1 2 50 690
2 1 40 590
2 2 41 585


It seems like a job for "aggregate", but I want to collapse on only cases 
where observation # < 3, and take the mean of a few vars in the aggregation. 
I can't seem to make it work, and didn't find examples that were on the 
mark. I think I'm suffering from "prospective interference" and my SPSS 
syntax knowledge to do exactly this is just getting in my way. 

any volunteers? I'd very grateful. Thanks!

-- 
---------------------------------------
David L. Van Brunt, Ph.D.
mailto:dlvanbrunt@gmail.com

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