Chris Rohlfs
>
> i'm trying to figure out the macro basics & can't seem to
> find any simple
> examples on the web or in the manual. if someone could
> please post the
> text of a simple *.do file that uses macros, i'd really
> really appreciate
> it. i'm using stata 7.
>
> i'd also really appreciate any suggestions on my specific
> problem that i'm
> trying to solve w/ macros:
>
> to take variables (air_reg1, air_reg2, ..., air_reg24)
> and (voc_reg1, ..., voc_reg24)
>
> and to produce the sum of the products:
>
> air_reg1*voc_reg1 + air_reg2*voc_reg2 + ... + air_reg24*voc_reg24
>
> for a bunch of different sets of variables ({air,voc} is
> one example) w/ a
> large dataset.
The second half of [U] is the most useful
section of the manual here.
For your example: One way to do it is
gen double sumproduct = 0
qui forval i = 1/24 {
replace sumproduct = sumproduct + air_reg`i' * voc_reg`i'
}
For one introduction to local macros as applied
to working through lists, there is a tutorial
in the Stata Journal
"How to face lists with fortitude"
Stata Journal 2(2):202--222 (2002)
If you do not subscribe to the Journal, and
naturally I recommend that, then the slides
of a talk on this material are accessible
at
http://fmwww.bc.edu/RePEc/usug2002/fortitude.pdf
or at
http://www.stata.com/support/meeting/8uk/fortitude.pdf
The recent thread on -foreach-, -forvalues- and -for-
started by Elizabeth Simantov on Monday 22 with the
heading
st: create many variables at once
and continuing through to Kit Baum on Thursday 25
with
st: Re: for vs foreach and forvalues
is also relevant.
-for- lovers would want me to point out
that your problem can also be done this way:
gen double sumproduct = 0
qui for var air_reg* \ var voc_reg* : replace sumproduct =
sumproduct + X * Y
assuming that -air_reg1-air_reg24- and the
corresponding -voc_reg*- are in that order in memory.
Note that this -for- solution does not use local
macros.
Nick
[email protected]
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
