with_index.rb

battle_cries = [{ king_leonidas: 'This is where we fight! This is where they die!' },
                { he_man: 'By the power of Greyskull... I have the powerrr!' },
                { sindel: 'You are pathetic and weak.' },
                { shang_tsung: 'Your soul is mine!' },
                { klingons: 'Today is a good day to die!' }]

def from_mortal_kombat?(battle_cry)
  [:sindel, :shang_tsung].include?(battle_cry.keys.first)
end

puts 'The old, ugly way. Well, at least for me.'
mortal_kombat_battle_cries = []
battle_cries.each_with_index do |battle_cry, index|
  if from_mortal_kombat?(battle_cry)
    mortal_kombat_battle_cries << [battle_cry, index]
  end
end

p mortal_kombat_battle_cries

puts 'New shiny way.'
mortal_kombat_battle_cries = battle_cries.each.with_index.map do |battle_cry, index|
  from_mortal_kombat?(battle_cry) ? [battle_cry, index] : nil
end.compact

p mortal_kombat_battle_cries

puts 'Or even like this if you like to inject.'
mortal_kombat_battle_cries = battle_cries.each.with_index.inject([]) do |memo, (battle_cry, index)|
  from_mortal_kombat?(battle_cry) ? memo << [battle_cry, index] : memo
end

p mortal_kombat_battle_cries