* chkdup -- a duplicate value identification program
* Marc Jacobs, University of Utrecht, The Netherlands
* October 1, 1991

program define chkdup
version 2.1
	mac def _varlist "req ex min(1) max(1)"
	parse "%_*"
	sort %_varlist
	capture by %_varlist: assert _N==1
	if _rc==0 { 
		di in gr "(%_varlist has no duplicate values)"
		exit
	}
	di _n in gr /*
*/ "duplicate values detected; the following values occur more than once:"
	confirm new var _DUPCNT
	capture { 
		by %_varlist: gen long _DUPCNT = _N if _n==1
		noisily list %_varlist _DUPCNT if _DUPCNT!=. & _DUPCNT>1, noo
	}
	mac def _rc=_rc
	capture drop _DUPCNT
	exit %_rc
end