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Re: st: cumulative average moving through time


From   Daniel Egan <dp.egan@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: cumulative average moving through time
Date   Wed, 6 Oct 2004 15:59:24 -0400

Hi Scott, 

by sort pid (ob):gen cave = sum(calc)/ob

This is so obvious as to be painful. So why didn't I think of it? 

1) Where/When did -sum()- become an acceptable argument to
-generate-!?!? I have only ever seen it in the context of -egen-.
Looking at the help for -generate-, there are no arguments that are
explicitly stated to be useable. It is only at the very bottom of the
examples that one sees an function -uniform-  and then -sum- used with
gen. Are the others?  I know that using many egen arguments with -gen-
will return errors (e.g. count).

2) Why does the ---bys pid (ob)-- do this correctly? I understand that
it is equivalet to --sort PID OB--, but why does it result in the
correct cumulative sum?
Another way of putting this is why doesnt -egen cave=sum(calc)/ob,
by(PID OB)- work if this does?

Sorry if this is a lot, I am just surprised about this. 

Oh, and thanks. I did not get to try Dan Lawson's code. 

Dan Egan
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