Dear Statalisters,
please excuse if this question is a bit wordy, but I have tried to be
as precise as possible to state my problem. I am writing a program
where I need to extract rows from a panel dataset, according to which
time periods and units the user specifies. Needless to say, any help
on this would be highly appreciated (I am new to Stata programming).
Here is my problem. The user has to tsset his data with panel and time
var. Then my program starts:
program dataprep , rclass
version 9.2
preserve
/* check if data is tsset with panel and time var and get these into locals */
/* (probably could be done more elegantly) */
qui tsset
if "`r(panelvar)'" == "" {
di as err "panel variable missing please use -tsset panelvar timevar"
exit 198
}
else {
local tvar `r(timevar)'
local pvar "`r(panelvar)'"
}
qui sort `pvar' `tvar'
/* Now the user enters a varlist and two numlists of integers for the
time periods and units he wants to use */
/* the numbers in these lists refer to the panel and time variable
used in tsset */
syntax varlist(ts min=2 numeric) , timex(numlist >=0 integer)
units(numlist integer)
tempvar YX
qui mkmat `varlist', matrix(`YX')
.
.
end
Now my question: How can I extract from the varlist (i.e. the matrix
YX) only those rows that the user specified in timex() and units().
So for example:
clear
use http://www.stata-press.com/data/r9/invest2.dta, clear
tsset company time
A panel dataset with 5 companies (1,...,5) and 20 time periods
(1,...,20). The user wants to use varibales invest, market and stock,
and wants to run the analysis using companies number 1, 2, and 4. And
time periods 3, 6, 7 and 9. Thus, she runs:
dataprep invest market stock, timex(3 6 7 9) units(1 2 4)
This will give me the three colum YX matrix
invest market stock
r1 317.60001 3078.5 2.8
r2 391.79999 4661.7002 52.599998
r3 410.60001 5387.1001 156.89999
r4 257.70001 2792.2 209.2
r5 330.79999 4313.2002 203.39999
r6 461.20001 4643.8999 207.2
r7 512 4551.2002 255.2
r8 448 3244.1001 303.70001
r9 499.60001 4053.7 264.10001
But now I want to extract from this matrix only the rows that
correspond to panelvar equal to 2,6,7, or 9 and time var equal to 1,2,
or 4. How can I do this?
NOTE: I cannot use the [if] or [in] statements to reduce the rows,
because in my full program the user needs to specify various timex,
timey, ... timez, and units and the YX matrix has to sliced in various
different ways.
Thank you very much!
Best,
Tom
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