Methods

The include? method returns a boolean indicating whether its argument is a key in the hash. has_key? and key? are synonyms of include?. The has_value? method returns a boolean indicating whether its argument is a value in the hash. value? is a synonym of has_value?.

a_hash_is_like_a_dictionary = {
  "Wittgenstein"=> "The power of language to make everything look the same
    which appears in its crassest form in the dictionary",
  Nabokov: "The reader should have a dictionary."
}

a_hash_is_like_a_dictionary.include?("Wittgenstein") #=> true
a_hash_is_like_a_dictionary.has_value?("Arthur the Aardvark") #=> false

The keys method returns an array of all the keys in its receiver. The values method returns an array of all the values. The length method returns the number of key-value pairs.

shorter_example_thankfully = {
  a: 0,
  b: 1,
  c: 2
}

shorter_example_thankfully.keys #=> [:a, :b, :c]
shorter_example_thankfully.values #=> [0, 1, 2]
shorter_example_thankfully.length #=> 3

The to_a method type converts its receiver hash into a nested array of [key, value] arrays. Conversely, one can type convert a nested array of two-element arrays to a hash with the to_h method.

hbo_shows_ranking = {
  "The Wire" => 1,
  "True Detective Season 1" => 2,
  "Westworld" => 3
}

hbo_shows_ranking.to_a #=> [["The Wire", 1], ["True Detective Season 1", 2], ["Westworld", 3]]

animated_ranking = [["South Park", 1], ["Rick and Morty", 2], ["Archer", 3]]
animated_ranking.to_h #=> {"South Park"=>1, "Rick and Morty"=>2, "Archer"=>3}