*设初始数据库只有id、date、weight三个变量。显示仅由观测所知的、任意连续30天内、体重变化超10斤的ID:
tempfile a
g d=date(date,"DM20Y")
form d %td
bys id (d): g i=_n
drop date
save `a',replace
ren weight weight1
ren d d1
bys id (d1): g n=_N
expandcl n,cl(id) gen(j)
bys id d1: replace i=_n
joinby id i using `a'
g a=(abs(d-d1)<=30)*(abs(weight-weight1)>=10)
collapse (sum)a,by(id)
n l id if a