r - Filter based on number of distinct values per group

Question

I have the following df:

names    sex
adam      M
jill      F
stewart   M
jordan    M
alica     F
jordan    F

How do I filter the rows so that I only get the names that are both M and F, in this case, jordan.

Answer 1

We can group by 'names' and filter the 'sex' having unique number of elements greater than 1

library(dplyr)
df %>% 
   group_by(names) %>%
   filter(n_distinct(sex) > 1)

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Or another option is to group by 'names' and filter the groups having both the 'M' and 'F'

df %>%
  group_by(names) %>%
  filter(all(c("M", "F") %in% sex))