Finding IDs based on one unique Output Value in R

Question

I have two columns in a dataframe advertisementID and Payout, Many advertisementID's have more than one Payout value, but I need to find those advertisementID's which have only one unique Payout value. How to do it in R ?

Example:

advertisementID   Payout  
      1              10  
      2              3  
      1              10  
      2              4 
      3              5
      3              4 

So the output should be like this:

advertisementID   Payout  
       1            10

as advertisementID 1 is having payout value unique which is 10

Answer 1

Using R base:

new <- aggregate(Payout ~ advertisementID, dt, unique) 
new[lengths(new$Payout)==1, ]

output:

  advertisementID Payout
1               1     10

Or in a cleaner way with magrittr:

library(magrittr)
aggregate(Payout ~ advertisementID, dt, unique) %>% subset(lengths(Payout)==1)