Contingency Tables from rows of matrices

Question

I have a dataframes that is a bootstrapped sample. This means some IDs have been repeated. Each dataframe contains 3 columns: ID, YEAR, Short_Rating.

My subsequent code requires the IDs to be unique. I need to rename the IDs and make them unique. For example I will have the following dataframe:

 ID              YEAR       Short_Rating
4205              1996          1
4205              1997          2
4205              1998          5        
4205              1999          2
2356              1996          3
2356              1997          4
2356              1998          1        
2356              1999          2
4205              1996          1
4205              1997          2
4205              1998          5        
4205              1999          2

I want it to rename the IDs in the ID column to:

   ID              YEAR       Short_Rating
    1              1996          1
    1              1997          2
    1              1998          5        
    1              1999          2
    2              1996          3
    2              1997          4
    2              1998          1        
    2              1999          2
    3              1996          1
    3              1997          2
    3              1998          5        
    3              1999          2

Each ID will always consist of the same number of years.