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

An alternative is to use the uniqueN function from data.table inside dplyr:

library(dplyr)
library(data.table)
a %>% summarise(count_all = n_distinct(A), count_BisY = uniqueN(A[B == 'Y']))

which gives:

  count_all count_BisY
1         3          2

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You can also do everything with data.table:

library(data.table)
setDT(a)[, .(count_all = uniqueN(A), count_BisY = uniqueN(A[B == 'Y']))]

which gives the same result.