Delete lines with older date

I have a spreadsheet with 2 columns : ID and Date .

Example :
ID1 1/01/2010
ID1 1/02/2010
ID1 1/03/2010
ID2 1/01/2011
ID2 1/02/2011

I need to have a list with only one line for each ID, namely the one with the most recent date :
ID1 1/03/2010
ID2 1/02/2011

How can I delete the other records (the Excel file contains + 15.000 records) ?