r - R：添加组内唯一值的计数，忽略数据框中的其他变量

Question

我想在我的数据框中添加一个新变量，对于每个组来说，它表示与一个变量（状态）相关的唯一条目的数量，而忽略其他变量。

数据输入

df <- data.frame(id=c(1,2,3,4,5,6,7,8,9),
                 state=c("CT","CT","AK","TX","TX","AZ","GA","TX","WA"),
                 group=c(1,1,2,3,3,3,4,4,4),
                 age=c(12,33,57,98,45,67,16,85,22)
                 )
df

期望的输出

want <- data.frame(id=c(1,2,3,4,5,6,7,8,9),
                 state=c("CT","CT","AK","TX","TX","AZ","GA","TX","WA"),
                 group=c(1,1,2,3,3,3,4,4,4),
                 age=c(12,33,57,98,45,67,16,85,22),
                 count=c(1,1,1,2,2,2,3,3,3)
                 )
want

Answer 1

我们需要一个小组n_distinct

library(dplyr)
df %>% 
  group_by(group) %>% 
  mutate(count = n_distinct(state)) %>%
  ungroup