Thank you, Nick. Indeed I have subscribed to this list for some time now,
and I have been able to learn a lot about Stata because of it. I do always
check the FAQ and the archived list postings before asking a question to the
list, but I suppose sometimes I just need a little help being directed to
the answers.
Again, thank you for your response. After looking through the FAQ you
suggested, I feel as though I now have a better understanding of the -egen,
group()- function.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Nick Cox
Sent: Monday, January 23, 2006 6:49 PM
To: [email protected]
Subject: st: RE: -group- within varlist
You have been on this list for some time and asked many questions, but it
doesn't seem that you are making much use of the help facilities, including
-search- and the FAQs.
I am not clear what the precise underlying question is here, but the answer
is definitely Yes.
There are many alternatives.
Much depends on what you mean by identifier. I take that to mean ideally
that each observation can be identified uniquely. If no such variable
exists, it can always be created with
. gen long id = _n
For much more discussion, see
FAQ . . . . . . . . . . . . . . . . . . . . . . Creating group
identifiers
3/01 How do I create individual identifiers numbered
from 1 upwards?
http://www.stata.com/support/faqs/data/group.html
As far as -egen, group()- is concerned, -by:- indeed can't be used with it.
But that functionality is completely unnecessary. If -by:- were allowed it
would just act if it were the first variable you specified. So whatever
variable you want as a -by:- argument should be the first named. So instead
of
. egen group = group(b a), by(c)
or
. by c: egen group = group(b a)
you just go
. egen group = group(c b a)
But -group()- generates grouping variables, which in general are not
identifiers.
Either way: -egen, group()- is just an application of -by:- in any case. For
more control in this and many other problems, you need to master -by:-
directly. There is a tutorial at
SJ-2-1 pr0004 . . . . . . . . . . Speaking Stata: How to move step by:
step
Q1/02 SJ 2(1):86-102 (no
commands)
explains the use of the by varlist : construct to tackle
a variety of problems with group structure, ranging from
simple calculations for each of several groups to more
advanced manipulations that use the built-in _n and _N
Nick
[email protected]
Terra Curtis
> Since the -egen- function -group- cannot be combined with "by", does
> anyone know if there is an alternative method (or Stata function) for
> creating an ID within a varlist?
>
> PS - I am using Stata 8.
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