This document discusses regular expressions and enumerables in Ruby. It covers the basics of regular expressions including syntax, characters that need to be escaped, and common patterns. It also demonstrates how to use regular expressions to scan, split, substitute, and match strings. The document then discusses enumerables and how collections in Ruby can use enumerable methods like each, map, grep, find, all?, and any? through the Enumerable module. It provides examples of using these methods on arrays and more complex data structures.

1. Class 4 Regular Expressions & Enumerables

2. Regular Expressions /regex will find me/

3. What are Regular Expressions Regular expressions allow matching and manipulation of textual data. Abbreviated as regex or regexp, or alternatively, just patterns

4. What are Regular Expressions For? Scan a string for multiple occurrences of a pattern. Replace part of a string with another string. Split a string based on a matching separator.

7. Regex Basics [abc] A single character: a, b or c [^abc] Any single character but a, b, or c [a-z] Any single character in the range a-z [a-zA-Z] Any single character in the range a-z or A-Z ^ Start of line $ End of line Start of string End of string

8. Regex Basics cont... . Any single character Any whitespace character Any non-whitespace character Any digit Any non-digit Any word character (letter, number, underscore) Any non-word character Any word boundary character

9. Regex Basics cont... (...) Capture everything enclosed (a|b) a or b a? Zero or one of a a* Zero or more of a a+ One or more of a a{3} Exactly 3 of a a{3,} 3 or more of a a{3,6} Between 3 and 6 of a

10. Regex: .match >> category = "power tools" => "power tools" >> puts "on Sale" if category.match(/power tools/) on Sale >> puts "on Sale" if /power tools/.match(category) on Sale

11. Regex: =~ >> category = "shoes" => "shoes" >> puts "15 % off" if category =~ /shoes/ 15 % off >> puts "15 % off" if /shoes/ =~ category 15 % off >> /pants/ =~ category => nil >> /shoes/ =~ category => 0 >> category = "women's shoes” >> /shoes/ =~ category => 8 8th character

12. Scan >> numbers = "one two three" => "one two three" >> numbers.scan(/+/) => ["one", "two", "three”]

13. Split with Regular Expressions >> "one twothree".split(//) => ["one", ”two", "three"]

14. gsub ”fred,mary,john".gsub(/fred/, “XXX”) => “XXX,mary,john”

15. gsub with a block "one twothree".gsub(/(+)/) do |w| puts w end one two three

16. Title Case Capitalize All Words of a Sentence: >> full_name.gsub(//){|s| s.upcase} => "Yukihiro Matsumoto"

17. Live Coding Example Scraping Thentic.com

18. Enumerables Collection Behavior

19. Why Use Enumerables Ruby's Enumerable module has methods for all kinds of tasks. 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.

20. 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

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

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

23. 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

24. 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

25. 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

26. 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"]

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

28. 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"

29. 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

30. 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

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

32. 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]

33. 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"]

34. 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"]

35. Homework Chapters: 10.1 – 10.8 11.1 -11.8