How to find number of unique ids corresponding to each date in a data drame

Question

I have a data frame that looks like this:

      date         time              id            datetime    
1 2015-01-02 14:27:22.130 999000000007628 2015-01-02 14         


        

Answer 1

Or we could use n_distinct from library(dplyr)

library(dplyr) 
df %>%
   group_by(date) %>%
   summarise(id=n_distinct(id))