Hash#&

hash.rb

class Hash
  # Intersection on hash keys (and values) that actually returns a Hash.
  # The RHS can be an Array or a Hash.
  #
  # == Examples:
  #  >> hsh = {:banana => "elephant", :bar => "foo", :baz => "wuux"}
  #  >> hsh & [:bar]
  #  => {:bar=>"foo"}
  #
  #  >> hsh & {:bar => "foo", :baz => "wuux"}
  #  => {:bar=>"foo", :baz=>"wuux"}
  #
  #  >> hsh & {:bar => "foo", :baz => 1}
  #  => {:bar=>"foo"}

  def &(array_or_hash)
    array_or_hash.inject({}) do |a, (k, v)|
      (!v || self[k] == v) ? a.merge(k => self[k]) : a
    end
  end
end