# Re: st: cumulative average moving through time

 From smerryman@kc.rr.com To statalist@hsphsun2.harvard.edu Subject Re: st: cumulative average moving through time Date Wed, 06 Oct 2004 15:33:52 -0500

```Dan,

1) It is listed [R]Functions.  -whelp mathfun- will list the other functions.

2) -bysort pid (ob)- sorts pid and then ob within pid but it performs the
-gen cave = sum(calc)/ob-  only on pid.  -bysort pid ob- would not work because
it would perform the calculation on each pid and ob pair.

I don't believe the –by- option in -egen- is flexible enough to interpret
-egen cave=sum(calc)/ob, by(pid ob)- correctly.  Also, -egen ,sum()- does not
allow expressions as sum(calc)/ob.

You might find Nick Cox's article "Speaking Stata:  How to move step by: step"

Scott

----- Original Message -----
From: Daniel Egan <dp.egan@gmail.com>
Date: Wednesday, October 6, 2004 2:59 pm
Subject: Re: st: cumulative average moving through time

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