How to remove duplicate values in one column by ID in R

Question

How to remove duplicate by ID. For each ID, the column Drug must have unique values. Any help is appreciated.

    dat <- read.table(text="Id  Drug    
A   Meropenem     
A   Ampicillin  
A   Augmentin 
A   Meropenem     
A   Ampicillin  
A   Augmentin
B   Meropenem     
B   Ampicillin    
B   Augmentin", header=TRUE)



This is the desired output: 
 
dat.desired <- read.table(text="Id  Drug
A   Meropenem     
A   Ampicillin  
A   Augmentin 
B   Meropenem     
B   Ampicillin    
B   Augmentin", header=TRUE)

Answer 1

Using the group_by in dplyr allows remove the duplicates per group only.

library(dplyr)
dat %>% group_by(Id) %>% filter( !duplicated(Drug))

  Id    Drug      
  <chr> <chr>     
1 A     Meropenem 
2 A     Ampicillin
3 A     Augmentin 
4 B     Meropenem 
5 B     Ampicillin
6 B     Augmentin