dplyr n_distinct with condition

Question

Using dplyr to summarise a dataset, I want to call n_distinct to count the number of unique occurrences in a column. However, I also want to do another summarise() for all uniqu

Answer 1

This produces the distinct A counts by each value of B using dplyr.

library(dplyr)
a %>%
  group_by(B) %>%
  summarise(count = n_distinct(A))

This produces the result:

Source: local data frame [2 x 2]

       B count
  (fctr) (int)
1      N     1
2      Y     2

To produce the desired output added above using dplyr, you can do the following:

a %>% summarise(count_all = n_distinct(A), count_BisY = length(unique(A[B == 'Y'])))

This produces the result:

  count_all count_BisY
1         3          2