(in R)如何根据b列排列A列

Question

我得到了这样一个数据帧:

d

我们可以从dplyr包中使用n_distinct:

library(dplyr)
df %>%
group_by(factory)%>%
summarise(bread = n_distinct(bread))

输出:

factory bread
<chr>   <int>
1 A           2
2 B           1
3 C           1

data.table选项

> setorder(setDT(df)[, .(Bread = uniqueN(Bread)), Factory], -Bread)[]
Factory Bread
1:       B     3
2:       A     1
3:       C     1
4:       D     1