How to combine information from multiple rows into one
 

Hi, I have a spreadsheet with multiple (duplicate) rows which I would like to
combine into one. The spreadsheet lists name/address of a customer and also
anyone else who may be living with them in the same property. I would like to
mail merge the file and send a letter to each customer listing who we think
lives in the property. Here is an example:

Current file:

Mr Peter Smith, 1 Nowhere Street, Amy Smith
Mr Peter Smith, 1 Nowhere Street, Tracey Smith
Mr Peter Smith, 1 Nowhere Street, Tim Smith

The new file should show 1 row as:

Mr Peter Smith, 1 Nowhere Street, Amy Smith, Tracey Smith, Tim Smith