Understanding Ruby's insertion sort algorithm - Honeybadger Developer Blog

There are lots of ways to sort data. The insertion sort algorithm is particularly interesting because it sorts the data in place and is easy to understand.Ruby's default sort method is not stable, so it does not preserve the relative order of elements with the same value. Both MRI's sort and sort_by methods can act at times as if they're stable, but it's a bad idea to rely on these methods if your code requires stable sorting. Otherwise, if all you need to do is sort singular elements with no duplicate entries that need to have their order preserved, you won't often need to reach further into your sorting toolbox. While it depends on the Ruby implementation, Ruby's default sort is often a form of quicksort. It has good performance as it stands, and you can read more about it at igvita.com.