st: problems with using preserve in looping

[ken first <kenscholar2008@gmail.com>]

Dear stata users,

I have two questions here and i hope someone can help.

1. I am wondering if someone knows about this strange thing with the
looping command. I used the below. sometimes it works and everything
runs smoothly and sometimes i get an error message. Does anyone know
what i did wrong here?

first i have

predict A, e

then

forvalue year = 1991/2011 {
preserve
keep if  year==`year'
gen B=A*matrix
restore
}

already preserved
r(621);



2. I need to use the below as there is a matrix that wont work if i
simply use if year==`year', but i would like to keep the results I
generated after everything has been restored. does anyone know what to
do?


first i have

predict A, e

then

forvalue year = 1991/2009 {
preserve
keep if  year==`year'
gen A=B*matrix   * i would like to keep the result here as a separate variable.
restore
}

Many thanks

Ken
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