duplicated() 有一个 data.frame 的方法，就是专门为这种类型设计的任务:

duplicated() has a method for data.frames, which is designed for just this sort of task:

df <- data.frame(a = c(1:4, 1:4), 
                 b = c(4:1, 4:1), 
                 d = LETTERS[1:8])

df[!duplicated(df[c("a", "b")]),]
#   a b d
# 1 1 4 A
# 2 2 3 B
# 3 3 2 C
# 4 4 1 D