Returning all maximum or minimum values that can be multiple

Question

Enumerable#max_by and Enumerable#min_by return one of the relevant elements (presumably the first one) when there are multiple max/min elements in the receiver. For example, the following:

[1, 2, 3, 5].max_by{|e| e % 3}

returns only 2 (or only 5).

Instead, I want to return all max/min elements and in an array. In the example above, it would be [2, 5] (or [5, 2]). What is the best way to get this?

Answer 1

arr = [1, 2, 3, 5]

arr.group_by{|a| a % 3} # => {1=>[1], 2=>[2, 5], 0=>[3]}
arr.group_by{|a| a % 3}.max.last # => [2, 5]