Need Google Spreadsheet Formula to get all same-postal code cities on a single row

Looking to get all same-postal code cities on a single row

On a sheet I have thousands of postal codes from Australia and the cities that are tied to those postal codes.

There are two main columns:

1. The Postal Codes
2. The cities that are part of those postal codes.

The postal codes repeat themselves, while the each of the cities are obviously unique. For example, postcode 2408 has 3 cities tied to it.

My problem is I can't come up with a formula to get the cities (that are tied to a unique postcode) names all into one cell. So the post code is on one column and the names of the cities are on another.

Any thoughts?