st: Re: understanding the difference between gen and egen

[Kit Baum <baum@bc.edu>]

Dick is caught by a historical issue here. Prior to Stata 9, you  
could say

gen foo = sum(bar)
egen foo = sum(bar)

which was indeed confusing, given that the gen produced a RUNNING sum  
and the egen produced a total. Wisely, Stata's developers renamed the  
egen function to total().

With respect to the wide array of non-official Stata capabilities  
(for the accessibility of which I am somewhat responsible) the Stata  
command findit will locate anything that is in the Stata Journal,  
Stata Technical Bulletin, or the SSC Archive which I maintain.  
Anything you find in the SSC Archive can be described with the ssc  
command, and installed likewise. Bill Gould's new official  
"adoupdate" command makes it as easy to keep user-installed stuff up  
to date as official Stata components. So yes, Stata is more confusing  
that a program fully described by a printed manual. Even official  
Stata is not fully documented by the version 9 manuals, given  
significant additions since 9.0. But "help whatsnew" and "help  
forthcoming" will assist with that.

Official Stata is a very dynamic organism, with significant  
enhancements during the life of a major version. When the user- 
written components made available through the Stata Journal and SSC  
Archive are taken into account, you literally have to check daily for  
what has been newly developed if you want to be fully au courant. (I  
added a number of new routines this week that had been in a backlog  
during my absence; "ssc whatsnew" will show them, with links to their  
descriptions). Admittedly this can be confusing; but it is also one  
of Stata's great virtues and comparative advantages over many  
alternative statistical languages.

PS> Confronted with 6 feet + of manuals on a shelf for Some  
Alternative Software, some users are comforted?

Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html


On Jun 14, 2006, at 2:33 AM, Dick wrote:


> I am now a confirmed Stata user and love it for all the reasons
> that Phil Schumm outlined the other day and more. But the recent
> note from a user regarding sums within id reminds me of how
> difficult it is sometimes for new users to get a handle on relatively
> simple things.  In the current case, if I look up "sum" in the master
> index, I am directed to -egen-. If I go to -egen-, somewhat  
> surprisingly,
> I don't find -sum- listed in the list of egen functions beginning  
> on page 101
> of the Data Management manual or summary of that list on page 105.
> Nor is it available in the drop down list of egen functions
> I can do -sum- as a function using -gen- but then I get a running  
> sum, not
> a total.
>
> It struck me that perhaps -help egenmore- would show me the sum  
> function.
> but no luck. A little further digging led me to the documentation  
> for the
> - -sum- function
> on page 157 which tells me that I can get a running sum and which  
> directs
> me to an "alternative sum function" in -egen-. What I did  
> eventually find in
> the documentation for -egen- was the -total- function which does  
> indeed
> produce a sum. But so does the -sum- function, so one is apparently an
> alias for the other.
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