*! version 1.0   STB-54: dm77
* 14Nov1999 by Duolao Wang
* London School of Hygiene and Tropical Medicine

program define unique1
	version 6
	syntax using/
	use `"`using'"',clear
unique0
end

program define unique0
	version 6
	local varlist " "
	parse "`*'"
	tempfile flag
	tempvar id byid

	quietly {
                gen `id'=_n
	          preserve
                sort `varlist'
                by `varlist': gen int `byid' = _n
                keep `id' `byid'
                sort `id'
                save `"`flag'"',replace
                restore, preserve
                merge using `"`flag'"'
                keep if `byid'==1 
                drop `id' `byid' _merge
                restore, not
      }
end