I want to separate the customers entering store by entering periods: who enter after t1/t2/t3 (different time). The following data are the all customers until the end of the time frame.
t1<-c(1:10) # at end of period t1,
t2<-c(1:7,12:15) #at the end of t2, id 1:7 from t1 stayed in the store and the rest of peopel from t1 left. but new customers with id 12:15 entered
t3<-c(3:9,12:14,20:25) # at end of t3, some in t1 stay and some in t2 stay and new people came.
enter2<-t2[!(t2 %in% t1)]
You can also use
setdiff to avoid the somewhat awkward
x[!x %in% y] construction:
enter3 <- t3[!((t3 %in%t1) | (t3%in% t2))] # using akrun's recommendation e2 = setdiff(t2, t1) e3 = setdiff(t3, union(t1, t2)) identical(enter2, e2) #  TRUE identical(enter3, e3) #  TRUE