假设我有两个data.tables:
summary <- data.table(period = c("A","B","C","D"),
from_date = ymd(c("2017-01-01", "2017-01-03", "2017-02-08", "2017-03-07")),
to_date = ymd(c("2017-01-31", "2017-04-01", "2017-03-08", "2017-05-01"))
)
log <- data.table(date = ymd(c("2017-01-03","2017-01-20","2017-02-01","2017-03-03",
"2017-03-15","2017-03-28","2017-04-03","2017-04-23")),
event1 = c(4,8,8,4,3,4,7,3), event2 = c(1,8,7,3,8,4,6,3))
看起来像这样:
> summary
period from_date to_date
1: A 2017-01-01 2017-01-31
2: B 2017-01-03 2017-04-01
3: C 2017-02-08 2017-03-08
4: D 2017-03-07 2017-05-01
> log
date event1 event2
1: 2017-01-03 4 1
2: 2017-01-20 8 8
3: 2017-02-01 8 7
4: 2017-03-03 4 3
5: 2017-03-15 3 8
6: 2017-03-28 …