program define genvsum
version 2.1
        if "%_*"=="" {
                di in red "invalid syntax -- see help genvmean"
                exit 198
        }
        mac def _varlist "req ex min(2)"
        mac def _in "opt"
        mac def _if "opt"
        mac def _options "Generate(str)"
        parse "%_*"
        mac def _g "%_generat"
        if "%_g"=="" { vmean }
        confirm new var %_g _NOBS
        capture {
                gen %_g = 0 %_if %_in
                gen long _NOBS = 0 %_if %_in
                parse "%_varlist", parse(" ")
                while "%_1"!="" {
                        replace %_g = %_g + cond(%_1==.,0,%_1) %_if %_in
                        replace _NOBS = _NOBS + cond(%_1==.,0,1) %_if %_in
                        mac shift
                }
                drop _NOBS
                exit
        }
        mac def _rc=_rc
        capture drop %_g
        capture drop _NOBS
        exit %_rc
end