Dear David and Ulrich,
Thank you for your advice.
You're definitely right.
I'm sorry I didn't include relevant statements, and I'm
impressed by your insight at the same time.
The original ones are:
foreach file in mat1982 mat1983 mat1984{
use `file'
foreach var of varlist A-D{
count if `var' == 0
local i = r(N)
local sum = `sum' + `i'
}
di `sum'
}
Things went well after modifying the 2nd line as
-use `file', clear-
Actually, I tried including -clear- in the loop, but at the
wrong place: just after -di `sum'-.
And that provoked another error message :-).
And the solution suggested by Ulrich,
>local sum 0
>foreach var of varlist A-D {
> count if `var' == 0
> local sum = `sum' + r(N)
>}
>di `sum'
is surely nicer than mine.
My solution, while ending without issuing no error messages,
produces some unwanted results.
That is, the cumulative sum for all the files are iteratively
calulated and shown, while Ulrich's return sums for each file
separately, and that's what I wanted.
I guess this is because `sum' is not initialized in each round
of the loop in mine, while it is in Ulrich's .
I learned a lot from this experience.
Thank you again.
K.I.
*
* 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/
