我有一个数据表:
library(data.table)
(f <- data.table(id1=c(1,2,3,1,2,3),
id2=as.factor(c("a","a","b","c","b","d")),
v=1:6,
key=c("id1","id2")))
id1 id2 v
1: 1 a 1
2: 1 c 4
3: 2 a 2
4: 2 b 5
5: 3 b 3
6: 3 d 6
> str(f)
Classes ‘data.table’ and 'data.frame': 6 obs. of 3 variables:
$ id1: num 1 1 2 2 3 3
$ id2: Factor w/ 4 levels "a","b","c","d": 1 3 1 2 2 4
$ v : int 1 4 2 5 3 6
- attr(*, …