Filter groups in dplyr that exclusively contain specific combinations of values

Question

Given a table like:

  id value
1  1     a
2  2     a
3  2     b
4  2     c
5  3     c

I would like to filter for:

a) the ids that only have value a, i.e. id 1.

b) the ids that contain a and b jointly, i.e. id 2.

Data:

data.frame(id = c(1,2,2,2,3), value = c("a", "a", "b", "c", "c"))

Answer 1

Try

a)

df %>% group_by(id) %>% filter(all(value == "a"))

b)

df %>% group_by(id) %>% filter(all(c("a", "b") %in% value))