如何使用dplyr汇总分组数据中的级别数（nlevels）？

Question

I would like to use the summarise function in dplyr to extract the number of levels for each variable in my data frame, after grouping. Here is a replicate of the data frame:

x=c("A","A","A","A","A","B","B","B","B","C","C","C","D","D","D","E","E")
y=c("a","b","c","a","b","a","b","c","d","c","b","e","b","d","f","a","b")
z=c("x","x","x","y","y","p","p","p","p","t","v","v","m","m","n","o","o")
d=data.frame(x,y,z)

Here is the code I am using

   library(dplyr)
   d %>%
   group_by(x) %>%
   summarise(total=n(),
          Y=nlevels(y),
          Z=nlevels(z))

But, this generates Y and Z columns that summarise the levels in the data frame 'd' rather than in the grouped data.

The data frame I would like to generate would look like this:

 x=c("A","B","C","D","E")
 total=c(5,4,3,3,2)
 Y=c(3,4,3,3,2)
 Z=c(2,1,2,2,1)
 d2=data.frame(x,total,Y,Z)
 d2

Thank you!

Answer 1

You need n_distinct for that:

d %>%
  group_by(x) %>%
  summarise(total = n(),
            Y = n_distinct(y),
            Z = n_distinct(z))

The result:

# A tibble: 5 x 4
       x total     Y     Z
  <fctr> <int> <int> <int>
1      A     5     3     2
2      B     4     4     1
3      C     3     3     2
4      D     3     3     2
5      E     2     2     1