Identifies rows that are in a baseline dataset but not in a comparator dataset
    
     
    identify_extra_rows(DS1, DS2, KEYS)
    
    Arguments
    
    
    
      | DS1 | Baseline dataset (data frame) | 
    
      | DS2 | Comparator dataset (data frame) | 
    
      | KEYS | List of variables that define a unique row within the datasets (strings) |