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Ruby Data Types

Ruby Data Types. and other languages… . Ruby Data Types: Array. Compare to Java/C++. Array literals/initialization a = [1,2,3] a2 = [-10..0, 0..10] a3 = [[1,2],[3,4]] a4 = [w*h, w, h] a5 = [] empty = Array.new zeros = Array.new(5, 0) Arrays are heterogeneous

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Ruby Data Types

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  1. Ruby Data Types and other languages…

  2. Ruby Data Types: Array Compare to Java/C++ • Array literals/initialization a = [1,2,3] a2 = [-10..0, 0..10] a3 = [[1,2],[3,4]] a4 = [w*h, w, h] a5 = [] empty = Array.new zeros = Array.new(5, 0) • Arrays are heterogeneous • length and size return # of elements • Access beyond end of array returns nil • Elements can be accessed similar to strings • Arrays can be dynamically resized (can assign past the end of the array) • Use | and & for union and intersection

  3. More arrays • words = %w[here we go again] => [‘here’,’we’,’go’,’again’] • Use << to append • Use * to replicate (e.g., a[0] * 3) • Useful functionality alphabet = ('A'..'Z').to_a alphabet.each {|c| print c } • Not covered: lots of methods, like clear, empty?, compact!, sort, sort!, pop, push, reverse, etc.

  4. Symbol Get used to symbols, they’re used a lot Immutable, interned string (only one copy) Colon-prefixed, e.g., :one Commonly used as hash key Also stores names of classes, methods and variables in symbol table – more efficient than storing as string, can be used with reflection If your code is using a string as a unique identifier, consider using a symbol instead Methods available to convert between string and symbol

  5. Hashes Required sometimes, e.g., Python Hashes supported directly in Perl, Python (dictionary) and Ruby and in class libraries of Java, C++ and C# Aka maps, associative arrays colors = { :Cyndi => "orange", :Karyl => "purple" } colors2 = { "Cyndi" => "orange", "Karyl" => "purple" } colors3 = { Cyndi: "orange", Karyl: "purple" } puts colors3[:Cyndi] colors.each do |key, value| puts "#{key}'s favorite color is #{value}" end Best to use immutable objects as keys Not covered: hash codes

  6. Array vs Hash Which is better if need to access items in order? Which is useful for direct access? Hash: useful for “paired” data

  7. Range parentheses required, else just applies to 3 Subrange introduced in Pascal, also used in Modula-2 and Ada. Others? • Purpose • determine if a value is in or out of range • iteration • Can be any value that implements <=> function (like CompareTo… why is this needed?) • 1..10 includes 10 • 1…10 excludes 10 coldwar = 1945..1989 coldwar.include? birthdate.year (1..3).to_a

  8. Booleans Compare to Java/C++/C TrueClass singleton, write as true FalseClass singleton, write as false nil means no value. Test directly (o == nil) or with nil? true != 1, false != 0

  9. Topic Summary • Language Concepts • Array • Heterogeneous? • Array operations • Fixed or dynamic size • Hash • key restrictions • Range • operations • Boolean • 0/1? • Ruby • Arrays • new • each • Symbols • Hashes • Range • Boolean

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