Cool tricks and expressive snippets with ruby collections/enumerables [closed]

Answer 1

My own are:

Initialize array elements with same expression:

5.times.map { some_expression }

Initialize array with same value:

[value]*5

Sum elements of an array:

[1,2,3].reduce(0, &:+)

Find all indices that match condition:

a.each_with_index.find_all { |e, i| some_predicate(e) }.map(&:last)