Given a data frame as follows:
给定数据框架如下:
id<-c(1,1,1,1,1,1,2,2,2,2,2,2)
t<-c(6,8,9,11,12,14,55,57,58,60,62,63)
p<-c("a","a","a","b","b","b","a","a","b","b","b","b")
df<-data.frame(id,t,p)
row id t p
1 1 6 a
2 1 8 a
3 1 9 a
4 1 11 b
5 1 12 b
6 1 14 b
7 2 55 a
8 2 57 a
9 2 58 b
10 2 60 b
11 2 62 b
12 2 63 b
id
