An idea for mapping to a hash. Kudos to @dorkalev.

map_hash.rb

# [1,2,3].map_hash { |x| [x, x*2] }                                                                                                                                     
# => {1=>2, 2=>4, 3=>6}
# { foo: "bar", fiz: "baz" }.map_hash { |k,v| [v,k] }                                                                                                                   
# => {"bar"=>:foo, "baz"=>:fiz}

module Enumerable
  def map_hash
    Hash[*self.inject([]) { |arr, a| arr += yield(a) }]
  end
end