Bug #11907
Updated by barelyknown (Sean Devine) over 8 years ago
**TL;DR Arrays with more than 6 items do not have their order preserved if sorted with sort_by and the sort_by block returns the same value for each.**
Let’s start with a simple array of 6 items and sort it by the same value using the sort_by method. In Ruby 2.3 and Ruby 2.2.3, the order of the list will remain the same.
```
list = [1,2,3,4,5,6]
list.sort_by { |item| nil }
=> [1,2,3,4,5,6]
```
But, let’s add one item.
```
list = [1,2,3,4,5,6,7]
# with Ruby 2.2.3
list.sort_by { |item| nil }
=> [1, 2, 3, 4, 5, 6, 7] 6]
# with Ruby 2.3.0
list.sort_by { |item| nil }
=> [4, 2, 3, 1, 5, 6, 7]
```
Whoa! In Ruby 2.3, the order of the first and fourth items will be swapped. And, if we have a list of 8 or more items, the order of the first and last items will be swapped.
```
list = [1,2,3,4,5,6,7,8]
list.sort_by { |item| nil }
=> [8, 2, 3, 4, 5, 6, 7, 1]
```