Ruby enumerable - find up to n occurrences of matching element

Question

I have the following array:

arr = [1, 3, 2, 5, 2, 4, 2, 2, 4, 4, 2, 2, 4, 2, 1, 5]

I want an array containing the first three odd elements.

I know I could do this:

arr.select(&:odd?).take(3)

but I want to avoid iterating through the whole array, and instead return once I've found the third match.

I came up with the following solution, which I believe does what I want:

my_arr.each_with_object([]) do |el, memo| 
  memo << el if el.odd?; break memo if memo.size == 3 
end

But is there a more simple/idiomatic way of doing this?

Answer 1

Use a lazy enumerator with Enumerable#lazy:

arr.lazy.select(&:odd?).take(3).force
# => [1, 3, 5]

force is used to force the lazy enumerator to evaluate. Or, you could use first as it's eager:

arr.lazy.select(&:odd?).first(3)
# => [1, 3, 5]