*-https://bbs.pinggu.org/thread-1245132-1-1.html

*-ramdom drop 200 obs

  clear
  set seed 13579
  set obs 10000
  gen income = rnormal(1500, 5000)
  count if income>1000&income<2000
  
  gen u = uniform() if income>1000&income<2000
  sort u
  gen n = _n
  
  drop if n<=200