Advanced Enumeration in

About Advanced Enumeration

More enumeration methods

In Enumeration, you were introduced to the count, any?, select, all and map enumeration methods. Here's a recap of those, with a few extras added:

fibonacci = [0, 1, 1, 2, 3, 5, 8, 13]

fibonacci.count  { |number| number == 1 }   #=> 2
fibonacci.any?   { |number| number > 20 }   #=> false
fibonacci.none?  { |number| number > 20 }   #=> true
fibonacci.select { |number| number.odd? }   #=> [1, 1, 3, 5, 13]
fibonacci.all?   { |number| number < 20 }   #=> true
fibonacci.map    { |number| number * 2  }   #=> [0, 2, 2, 4, 6, 10, 16, 26]
fibonacci.select { |number| number >= 5}    #=> [5, 8, 13]
fibonacci.find   { |number| number >= 5}    #=> 5

# Some methods work with or without a block
fibonacci.sum  #=> 33
fibonacci.sum {| number | number * number }  #=> 273

# There are also methods to help with nested arrays:
animals = [ ['cat', 'bob'], ['horse', 'caris'], ['mouse', 'arya'] ]
animals.flatten  #=> ["cat", "bob", "horse", "caris", "mouse", "arya"]

Enumerating Hashes

Enumerating Hash objects is exactly the same as enumerating Array objects, except that the block receives two arguments: the key and the value:

pet_names = {cat: "bob", horse: "caris", mouse: "arya"}
pet_names.each { |animal, name| ... }

If you only need one of the values, you can use the special _ symbol to indicate that one value is not needed. This helps both in terms of developer clarity and also is a performance optimisation.

pet_names = {cat: "bob", horse: "caris", mouse: "arya"}
pet_names.map { |_, name| name }  #=> ["bob, "caris", "arya"]

Nested Enumerations

You can also enumerate in nested blocks, and daisy chain methods together. For example, if we have an array of hashes of animals, and we want extract the animals with short names, we might want to do something like:

pets = [
  { animal: "cats", names: ["bob", "fred", "sandra"] },
  { animal: "horses", names: ["caris", "black beard", "speedy"] },
  { animal: "mice", names: ["arya", "jerry"] }
]

pets.map { |pet|
  pet[:names].select { |name| name.length <= 5 }
}.flatten.sort
#=> ["arya", "bob", "caris", "fred", "jerry"]