Enumerables
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The document discusses the Enumerable module in Ruby, which provides collection-oriented methods like each, map, grep, find, all?, any?, and inject. It explains that classes like Array, Hash, and a custom MyCollection class can mix in Enumerable to gain these collection methods. It provides examples of using Enumerable methods on a vehicles array to select, transform, and iterate over elements in complex ways.
![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](https://image.slidesharecdn.com/enumerables-110304183008-phpapp01/85/Enumerables-7-320.jpg)
![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](https://image.slidesharecdn.com/enumerables-110304183008-phpapp01/85/Enumerables-9-320.jpg)
![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"]](https://image.slidesharecdn.com/enumerables-110304183008-phpapp01/85/Enumerables-10-320.jpg)
![GREP
• The grep method 'searches' for members using a regular
expression.
>> v_names.grep /a/
=> ["car"]
>> v_names.grep(/a/) { |v| v.upcase}
=> ["CAR"]](https://image.slidesharecdn.com/enumerables-110304183008-phpapp01/85/Enumerables-11-320.jpg)
![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]](https://image.slidesharecdn.com/enumerables-110304183008-phpapp01/85/Enumerables-16-320.jpg)
![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"]](https://image.slidesharecdn.com/enumerables-110304183008-phpapp01/85/Enumerables-17-320.jpg)
![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"]](https://image.slidesharecdn.com/enumerables-110304183008-phpapp01/85/Enumerables-18-320.jpg)
Enumerables
- 1. ENUMERABLE A powerful Ruby Module for Collections
- 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
- 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"]