sorting - What is the benefit for a sort algorithm to be stable?

Question

A sort is said to be stable if it maintains the relative order of elements with equal keys. I guess my question is really, what is the benefit of maintaining this relative order? Can someone give an example? Thanks.

Answer 1

It enables your sort to 'chain' through multiple conditions.

Say you have a table with first and last names in random order. If you sort by first name, and then by last name, the stable sorting algorithm will ensure people with the same last name are sorted by first name.

For example:

• Smith, Alfred
• Smith, Zed

Will be guaranteed to be in the correct order.