three different ways to create a list from another list

list_comprehensions.rb

require 'benchmark'

@arr = (1..100000).to_a


def rookie_way
  new_arr = []
  @arr.each do |x|
    if x % 2 == 0
      new_arr << x * 3 if x * 3 < 20
    end
  end
  new_arr
end

def chainsaw
  @arr.select{|x| x % 2 == 0 }.map{|x| x * 3}.reject{|x| x > 19}
end


def in_between
  @arr.map{|x| x * 3 if x % 2 == 0 && x * 3 < 20}.compact
end


r = 100

Benchmark.bmbm do |bm|
  bm.report(:rookie_way) { rookie_way }
  bm.report(:chainsaw) { chainsaw }
  bm.report(:in_between) { in_between }
end