Web Science Stream

1. Web Science Stream Introducing Ruby

2. What is Ruby? • Originated in Japan in 1995 and it was created by Yakihiro Matsumoto • High level programming language • Scripting language which is interpreted • Object Oriented

3. What about performance? • Code caching • Caching the output of a script for reuse rather than executing the script every time • Persistent interpreters • Loading the interpreter once and keeping it running • What about your performance when developing an application?

4. What about OOP? • Program made of objects capable of communicating with other objects • Each object can store data internally • Objects with similar characteristics are instances of the same class

5. Interactive Ruby Shell • The shell where we can input ruby commands Note: In windows we won’t be using a standard DOS box but use the “Open Ruby Console Window” from the Instant Rails application

6. As easy as 1, 2, 3 • Open a Ruby Console Window • Type “irb” • And we’re ready to start ... • Type “1” • Type “2” • Type “3” • What is the result? • Is it the same?

7. In Ruby everything is an object! • The result might look the same as the input but • Its not the same number • The output is a Ruby object • As a proof, type • 1.class • What’s the result?

8. More and more classes 1.class • Fixnum What if we try Fixnum.class

9. The world is full of numbers ... • 1 + 2 • 4 – 3 • 3 / 2 (Integers) • 3.0 / 2.0 (Floats) • 3 ** 2 (3 to the power of 2) • 5 % 2 (5 remainder 2) • 17_000_000_000_000_000_000 (What’s the effect of the underscore?) • 1.7e19

10. Numbering exercises 1. What’s the result of 17_000_000_000_000_000_000 == 1.7e19 2. What happens when you write googol = 10.0 ** 100 googolplex = 10.0 ** googol

11. Literal objects • Strings or numbers that appear directly in the code • String literal Irb> “The dog ate a bone” => “The dog ate a bone” Irb> “The dog ate a bone”.class => String Irb> “The dog ate a bone”.length => 18

12. Even more strings ... • “Hello “ + “World” • “hi “ * 3 • “1” + “2” • “1” * 2 • “Hello”.capitalize • “Hello”.reverse • “Hello”.upcase • “Hello”.downcase • “Hello”.swapcase • “a”.next • “aa”.next

13. String exercise • "hello".length + "world".length • "".empty? • "Zoo".include? "oo" • "cats".chop • How do you display your name backwards?

14. Easy conversions ... • Convert anything to ... • .to_s String • .to_i Integer • .to_f Float • What’s the result of ... • 2.to_s

15. Variables • Name of an object • city = “Valletta” • Variables always start with a lowercase letter

16. Constants • Name of an object • City = “Valletta” • Constants always start with an uppercase letter • Constants should not change, if you try Ruby will send a warning • Try • City = “Valletta” • City = “Mdina”

17. Shortcuts

18. Our first program Create a first.rb file and type the following ... name = “Tom” puts “Hello “ + name + “. How are you?” no1 = 2 no2 = 4 no3 = no1 + no2 puts “The answer is “ + no3.to_s

19. Some tips and conventions • Please use meaningful names for variables ... • age vrs a • Use the following approach with Multiwords • studentAge or student_age vrs studentage • Don’t be afraid to use constants where values don’t change • Use irb when you need to test small sections of code • When you need help use ri XXXX • Eg ri String • Eg ri String#upcase

20. Loops 4.times do puts “Hello” end Exercise What is the sum of all the integers from 1 to 1000?

21. Getting user input name = gets To remove any carriage returns or new lines use chomp “Alexiei\n”.chomp

22. Input exercise • Write a small program which asks for your age, calculates the year you were born and displays: You were born in 19XX

23. Conditions if city == “Valletta" licence = “V Licence” else licence = “normal” end = is an assignment == is a boolean comparison

24. Conditions if city == “Valletta" licence = “V Licence” elsifcity == “Mdina” licence = “M Licence” else licence = “normal” end Note that only the first elsif that returns true gets executed

25. Comparisons • ==equal • !=not equal to • >greater than • <less than • >=greater than or equal to • <=less than or equal to

26. String comparison “9” < “D” “a” < “b” “h” == “h” “H” == “h” “Z” <= “b” “j” != “r”

27. While loop count = 0 while count < 10 count += 1 end

28. More tips and conventions • Use proper indentation • Write comments when needed # I’m a comment and can write whatever i want

29. Arrays >> numbers = [ "zero", "one", "two", "three", "four" ] => ["zero", "one", "two", "three", "four"] >> numbers.class => Array >> numbers[0] => "zero"

30. Fun with Arrays names = [ "Melissa", "Daniel", "Samantha", "Jeffrey"] What about ... names.sort names.reverse names.length names + [“Tom”] names - [“Daniel”] names * 2 puts names.to_s

31. Let’s iterate names.each do |friend| puts “I have a friend called “ + friend end What about using 4.times or ... names.length.times do |i| puts "I have a friend called " + names[i] end What if I want to print my friends in sorted order?

32. What’s in a Hash? addressBook = { “Valletta" => “Tom", “Sliema" => “Jack", “Mdina" => “Ben” }

33. Iterating Hashes addressBook.each do |key, value| puts key + " => " + value end There is also ... addressBook.each_key do |key| addressBook.each_value do |value|

34. Functions ... • Not associated with any other object def say_hi puts "Hello, How are you?" end say_hi

35. Function parameters ... def say_hi(name) puts "Hello " + name + ", How are you?" end say_hi("Daniel") say_hi "Sandy"

36. Classes • The class keyword defines a class • By defining a method inside this class, we are associating it with this class • The initialize method is what actually constructs the data structure. Every class must contain an initialize method. • The @ sign in front of variables distinguishes the variable as an object variable.

37. Example class class Address def initialize(street) @street = street end end address = Address.new(“2 Republic Str")

38. Example class with return class Address definitialize(street) @street = street end def street @street end end >> address.street => " 2 Republic Str"

39. Shortcut to class with return class Address def attr_reader: street initialize(street) @street = street end end

40. Shortcut to set a variable class Address def attr_reader: street attr_writer: street initialize(street) @street = street end end

41. Shortcut to getting and setting a variable in one go class Address def attr_accessor: street initialize(street) @street = street end end

42. Private vrs Public classes class SomeClass def method1 # default to public ... end private # subsequent methods are private. def method2 # private method ... end def method3 # private method ... end public # Set back to public. def method4 # public method ... end end

43. Using classes • Save them in a className.rb file • Make use of the following command require “className“ • Just use the classes normally

44. Some final guidelines • If you can't sumarize in one sentence what the function does, it's probably too complicated • If you have to scroll to see the entire function, it is too long • Studies suggest that a person can only keep track of at most 7 or so things at one time. If your function has more than 5 or 6 variables, it is probably too long.

45. Questions?