How to include conditions in program (.ado file)

[Magnus Haselier]

Hi,

I am very new to writing programs in Stata. My current project is to write an ado-file to get the mean of a variable conditional on a time period (I know this is already possible with built in commands).
I have the following dataset and want to calculate the mean price for a specified time period.

year price
2002 20
2003 21
2004 19
2005 18
2006 21
2007 22
2008 20
2009 21

so in the end I want to type for example progname price if inrange(year,2004,2008) to get the mean price between 2004 and 2008. (Actually the program is supposed to give me means, 95ci and export everything to excel, but one problem at a time).

What I cannot figure out is how to get the if-condition into the program.
The basic version from where I started is:

cap program drop pmean
program pmean, rclass
        version 15
        syntax varlist [if] [in]
        
        qui sum `1'
        return list
end

where in the program do I specify the year(s) and how would you suggest to do it?

Thank you for your help
Kind regards

Magnus

[Stephen Jenkins]

Using viewsource, have a look at someone else's ado-file (including StataCorp's) and you'll virtually always see creation of a temporary "touse" variable (and you'll see how its done, and takes account of if and in too). Then all commands like your summarize one have "if `touse'" appended to them so that the appropriate sample is used

[Magnus Haselier]

Stephen Jenkins thank you, I'll give that a try