小编use*_*088的帖子

给定如下数据结构:

set.seed(10)
fruits <- c("apple", "orange", "pineapple")
fruits2 <- data.frame(id = 1:10, fruit1 = sample(fruits, 10, replace = T), fruit2 =   sample(fruits, 10, replace = T), fruit3 = sample(fruits, 10, replace = T))

> fruits2
   id    fruit1    fruit2    fruit3
1   1    orange    orange pineapple
2   2     apple    orange    orange
3   3    orange     apple pineapple
4   4 pineapple    orange    orange
5   5     apple    orange    orange
6   6     apple    orange pineapple
7   7     apple     apple pineapple
8   8     apple     apple     apple
9 …