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

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]