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RE: st: How to insert scalars (elements from Stata's matricies) as locals' values in the 'forvalues' command?


From   Charalambos Karagiannakis <karagiannakis.charalambos@ucy.ac.cy>
To   statalist@hsphsun2.harvard.edu
Subject   RE: st: How to insert scalars (elements from Stata's matricies) as locals' values in the 'forvalues' command?
Date   Mon, 22 Oct 2012 12:38:31 +0300

Dear Maarten and Nick, thank you very much for your help. As Mr. Nick
described, the new variable I would like to create is not aligned with the
original data. Off course I could have done it using vectors so that not to
mess with the dataset, but for a couple of reasons I decided to do it this
way.

Charalampos K. 


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: Friday, October 19, 2012 2:29 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: How to insert scalars (elements from Stata's matricies) as
locals' values in the 'forvalues' command?

Maarten's bottom line is key. To expand on that, there are two over-arching
points here:

1. For reduction to means of groups, -egen-'s -mean()- function with
-by:- gets you there in one line. There is no need to write a loop.
(Actually, you could do this without a loop even if -egen- didn't exist, as
the code of -_gmean.ado- will show.)

2. Charalambos is writing the means in observations 1 up, so that they are
not aligned with the original data. That's a kind of spreadsheet thinking,
it seems to me. There may be a good reason for this, but for most purposes
it's better to align group summaries with the original data, even though
they are repeated for each observation in the group.
-egen-'s -tag()- function offers an easy route to selecting one value from
each group when that is what is wanted.

Nick

On Fri, Oct 19, 2012 at 8:34 AM, Maarten Buis <maartenlbuis@gmail.com>
wrote:
> On Fri, Oct 19, 2012 at 9:19 AM, Charalambos Karagiannakis wrote:
>> sum time_quarter
>> forvalues i = [r(min)](1)[r(max)] {
>
> The way to make that work is:
>
> forvalues i = `r(min)'(1)`r(max)' {
>
> or:
>
> forvalues i = `r(min)/`r(max)' {
>
> However, I suspect that you are much better of not running that loop 
> at all and instead look at the -by- prefix in combination with -egen-.
>
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