Ruby's Enumerable module

1. A powerful Ruby Module for Collections Enumerable by Sarah Allen and Liah Hansen

2. Why Use Enumerables Ruby's Enumerable module has methods for all kinds of tasks which operate on a collection. If you can imagine a use for the #each method other than simply iterating, there is a good chance a method exists to do what you have in mind.

3. What does Enumerable Mean? Collection objects (instances of Array, Hash, etc) typically “mixin” the Enumerable module The Enumerable module gives objects of collection classes additional collection-specific behaviors. The class requiring the Enumerable module must have an #each method because the additional collection-specific behaviors given by Enumerable are defined in terms of #each

4. Mixing in Enumerable class MyCollection include Enumerable #lots of code def each #more code end end

5. View all Classes Mixing in Enumerable ObjectSpace.each_object(Class) do |cl| puts cl if cl < Enumerable end

6. Enumerable::Enumerator Struct::Tms Dir File IO Range Struct Hash Array String Struct::Group Struct::Passwd MyCollection StringIO Gem::SourceIndex YAML::Set YAML::Pairs YAML::Omap YAML::SpecialHas

7. Test an Instance or Class >> a = [1,2,3] => [1, 2, 3] >> a.respond_to? :any? => true >> a.is_a? Enumerable => true >> Array < Enumerable => true

8. Enumerable Methods Collection Behavior

9. each Classes that include the Enumerable module must have an #each method. The #each method yields items to a supplied code block, one at a time Different Classes define #each differently Array: #each yields each element Hash: each yields #each key/value pair as a two-element array >> v_names = %w(car truck bike) => ["car", "truck", "bike"] >> v_names.each do |vehicle| ?> puts vehicle >> end

10. map The map method modifies each member according to instructions in a block and returns the modified collection of members. >> v_names.map { |v| v.upcase} => ["CAR", "TRUCK", "BIKE"]

11. grep The grep method 'searches' for members using a regular expression. >> v_names.grep /a/ => ["car"] >> v_names.grep(/a/) { |v| v.upcase} => ["CAR"]

12. find >> v_names.find { |v| v.size > 3} => "truck" >> v_names.find { |v| v.size > 2} => "car" >> v_names.find do |v| v.size > 3 && v.size < 5 end => "bike"

13. all? The all? method returns true if all of the members of a collection satisfy the evaluation of the block. Otherwise it returns false. >> v_names.all? { |v| v.length > 2} => true >> v_names.all? { |v| v.length > 10} => false

14. any? The any? method returns true if any of the members of a collection satisfy the evaluation of the block. Otherwise it returns false. >> v_names.any? { |v| v.length == 3} => true >> v_names.any? { |v| v = "car"} => true

15. Working with Complex Data irb >> load 'vehicles.rb' => true

16. inject >> $vehicles.inject(0) do |total_wheels, v| ?> total_wheels += v[:wheels] >> end => 10 >> $vehicles.inject([]) do |classes, v| ?> classes += v[:classes] >> end.uniq => [:ground, :water, :air]

17. Complex Operations >> $vehicles.find do |v| ?> v[:name] =~ /Plane/ >> end[:name] => "Plane" >> $vehicles.find_all do |v| ?> v[:name] =~ /Plane/ >> end.collect { |v| v[:name] } => ["Plane", "Sea Plane"] >> $vehicles.find_all do |v| ?> v[:wheels] > 0 >> end.collect { |v| v[:name] } => ["Car", "Truck", "Bike"]

18. Complex Operations Continued >> $vehicles.find_all do |v| ?> v[:classes].include? :ground >> end.collect { |v| v[:name] } => ["Car", "Truck", "Bike", "Sea Plane"] >> $vehicles.find_all do |v| ?> v[:classes].include? :air >> end.collect { |v| v[:name] } => ["Plane", "Helicopter", "Sea Plane"]