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class Hash examples

---

grades = Hash.new
grades = Hash.new(0)
grades = {"Timmy Doe" => 8} 
grades.default = 0
grades = { "Jane Doe" => 10, "Jim Doe" => 6 }
grades["Dorothy Doe"] = 9
puts grades["Jane Doe"] # => 10

options = { :font_size => 10, :font_family => "Arial" }
options = { font_size: 10, font_family: "Arial" }
options[:font_size] # => 10

books = {} 
books[:matz] = "The Ruby Language" 
books[:black] = "The Well-Grounded Rubyist"

class Book 
  attr_reader :author, :title 
  def initialize(author, title) 
    @author = author 
    @title = title 
  end 

  def ==(other) 
    self.class === other and 
      other.author == @author and 
      other.title == @title 
  end 

  alias eql? == 

  def hash
    @author.hash ^ @title.hash # XOR 
  end 
end 

book1 = Book.new 'matz', 'Ruby in a Nutshell' 
book2 = Book.new 'matz', 'Ruby in a Nutshell' 
reviews = {} 
reviews[book1] = 'Great reference!' 
reviews[book2] = 'Nice and compact!' 
reviews.length #=> 1

puts Hash["a", 100, "b", 200].inspect #=> {"a"=>100, "b"=>200} 
puts Hash[ [ ["a", 100], ["b", 200] ] ].inspect #=> {"a"=>100, "b"=>200} 
puts Hash["a" => 100, "b" => 200].inspect #=> {"a"=>100, "b"=>200}

h = Hash.new("Go Fish") 
h["a"] = 100 
h["b"] = 200 
puts h["a"].inspect #=> 100 
puts h["c"].inspect #=> "Go Fish"

puts h["c"].upcase!.inspect #=> "GO FISH" 
puts h["d"].inspect #=> "GO FISH" 
puts h.keys.inspect #=> ["a", "b"]

h = Hash.new { |hash, key| hash[key] = "Go Fish: #{key}" } 
puts h["c"].inspect #=> "Go Fish: c" 
puts h["c"].upcase!.inspect #=> "GO FISH: C" 
puts h["d"].inspect #=> "Go Fish: d" 
puts h.keys.inspect #=> ["c", "d"]

puts Hash.try_convert({1=>2}).inspect # => {1=>2} 
puts Hash.try_convert("1=>2").inspect # => nil

h1 = { "a" => 1, "c" => 2 } 
h2 = { 7 => 35, "c" => 2, "a" => 1 } 
h3 = { "a" => 1, "c" => 2, 7 => 35 } 
h4 = { "a" => 1, "d" => 2, "f" => 35 } 
puts (h1 == h2).inspect #=> false 
puts (h2 == h3).inspect #=> true 
puts (h3 == h4).inspect #=> false

h = { "a" => 100, "b" => 200 } 
puts h["a"] #=> 100 
puts h["c"] #=> nil

h = { "a" => 100, "b" => 200 } 
h["a"] = 9 
h["c"] = 4 
puts h.inspect #=> {"a"=>9, "b"=>200, "c"=>4} 
puts h.store("d", 42).inspect #=> {"a"=>9, "b"=>200, "c"=>4, "d"=>42}

a = "a" 
b = "b".freeze 
h = { a => 100, b => 200 } 
puts (h.key(100).equal? a).inspect #=> false 
puts (h.key(200).equal? b).inspect #=> true

h = {"colors" => ["red", "blue", "green"], "letters" => ["a", "b", "c" ]} 
puts h.assoc("letters").inspect #=> ["letters", ["a", "b", "c"]] 
puts h.assoc("foo").inspect #=> nil

h = { "a" => 100, "b" => 200 } 
puts h.inspect #=> {"a"=>100, "b"=>200} 
puts h.clear.inspect #=> {}

h1 = { "a" => 100, "b" => 200, :c => "c" } 
puts h1["a"].inspect #=> 100 
puts h1.compare_by_identity 
puts h1.compare_by_identity? #=> true 
puts h1["a"].inspect #=> nil # different objects. 
puts h1[:c].inspect #=> "c" # same symbols are all same.

h = Hash.new 
puts h.inspect #=> {} 
puts h.default.inspect #=> nil 
puts h.default(2).inspect #=> nil

h = Hash.new("cat") 
puts h.inspect #=> {} 
puts h.default.inspect #=> "cat" 
puts h.default(2).inspect #=> "cat"

h = Hash.new {|h,k| h[k] = k.to_i*10} 
puts h.inspect #=> {} 
puts h.default.inspect #=> nil 
puts h.default(2).inspect #=> 20

h = { "a" => 100, "b" => 200 } 
h.default = "Go fish" 
puts h["a"].inspect #=> 100 
puts h["z"].inspect #=> "Go fish"

h = Hash.new {|h,k| h[k] = k*k } 
puts h.inspect #=> {} 
p = h.default_proc  
a = [] 
puts a.inspect #=> [] 
p.call(a, 2) 
puts a.inspect #=> [nil, nil, 4]

h.default_proc = proc do |hash, key| 
  hash[key] = key + key 
end 
puts h[2].inspect #=> 4 
puts h["cat"].inspect #=> "catcat"

h = { "a" => 100, "b" => 200 } 
puts h.delete("a").inspect #=> 100 
puts h.delete("z").inspect #=> nil 
puts h.delete("z") { |el| "#{el} not found" }.inspect #=> "z not found"

h = { "a" => 100, "b" => 200, "c" => 300 } 
puts h.delete_if {|key, value| key >= "b" }.inspect #=> {"a"=>100}

h.each {|key, value| puts "#{key} is #{value}" }

h.each_key {|key| puts key }

h.each_pair {|key, value| puts "#{key} is #{value}" }

h.each_value {|value| puts value }

puts {}.empty? #=> true

puts h.fetch("a").inspect #=> 100 
puts h.fetch("z", "go fish").inspect #=> "go fish" 
puts h.fetch("z") { |el| "go fish, #{el}"}.inspect #=> "go fish, z"
# puts h.fetch("z").inspect

a = {1=> "one", 2 => [2,"two"], 3 => "three"} 
puts a.flatten.inspect # => [1, "one", 2, [2, "two"], 3, "three"] 
puts a.flatten(2).inspect # => [1, "one", 2, 2, "two", 3, "three"]

puts h.has_key?("a").inspect #=> true 
puts h.has_key?("z").inspect #=> false

puts h.has_value?(100).inspect #=> true 
puts h.has_value?(999).inspect #=> false

puts h.include?("a").inspect #=> true 
puts h.include?("z").inspect #=> false

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300 } 
puts h.inspect #=> "{\"c\"=>300, \"a\"=>100, \"d\"=>400}"

h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 } 
puts h.invert.inspect #=> {0=>"a", 100=>"m", 200=>"d", 300=>"y"}

h = { "a" => 100, "b" => 200, "c" => 300, "d" => 300 } 
puts h.key(200).inspect #=> "b" 
puts h.key(300).inspect #=> "c" 
puts h.key(999).inspect #=> nil

puts h.key?("a").inspect #=> true 
puts h.key?("z").inspect #=> false

puts h.keys.inspect #=> ["a", "b", "c", "d"]

puts h.length.inspect #=> 4 
puts h.delete("a").inspect #=> 200 
puts h.length.inspect #=> 3

puts h.member?("a").inspect #=> false 
puts h.member?("z").inspect #=> false

h1 = { "a" => 100, "b" => 200 } 
h2 = { "b" => 254, "c" => 300 } 
puts h1.merge(h2).inspect #=> {"a"=>100, "b"=>254, "c"=>300} 
puts h1.merge(h2){|key, oldval, newval| newval - oldval}.inspect #=> {"a"=>100, "b"=>54, "c"=>300} 
puts h1.inspect #=> {"a"=>100, "b"=>200}

h1 = { "a" => 100, "b" => 200 } 
h2 = { "b" => 254, "c" => 300 } 
puts h1.merge!(h2).inspect #=> {"a"=>100, "b"=>254, "c"=>300} 
h1 = { "a" => 100, "b" => 200 } 
h2 = { "b" => 254, "c" => 300 } 
puts h1.merge!(h2) { |key, v1, v2| v1 }.inspect #=> {"a"=>100, "b"=>200, "c"=>300}

a = {1=> "one", 2 => "two", 3 => "three", "ii" => "two"} 
puts a.rassoc("two").inspect #=> [2, "two"] 
puts a.rassoc("four").inspect #=> nil

a = [ "a", "b" ] 
c = [ "c", "d" ] 
h = { a => 100, c => 300 } 
puts h[a].inspect #=> 100 
a[0] = "z" 
puts h[a].inspect #=> nil 
puts h.rehash.inspect #=> {["z", "b"]=>100, ["c", "d"]=>300} 
puts h[a].inspect #=> 100

h = { "a" => 100, "b" => 200, "c" => 300 }
puts h.reject {|k,v| k < "b"}.inspect #=> {"b" => 200, "c" => 300} 
puts h.reject {|k,v| v > 100}.inspect #=> {"a" => 100}

puts h.replace({ "c" => 300, "d" => 400 }).inspect #=> {"c"=>300, "d"=>400}

h = { "a" => 100, "b" => 200, "c" => 300 } 
puts h.select {|k,v| k > "a"}.inspect #=> {"b" => 200, "c" => 300} 
puts h.select {|k,v| v < 200}.inspect #=> {"a" => 100}

h = { 1 => "a", 2 => "b", 3 => "c" } 
puts h.shift.inspect #=> [1, "a"] 
puts h.inspect #=> {2=>"b", 3=>"c"}

h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 } 
puts h.length.inspect #=> 4 
puts h.delete("a").inspect #=> 200 
puts h.length.inspect #=> 3

h = { "a" => 100, "b" => 200 } 
h["a"] = 9 
h["c"] = 4 
puts h.inspect #=> {"a"=>9, "b"=>200, "c"=>4} 
puts h.store("d", 42).inspect #=> {"a"=>9, "b"=>200, "c"=>4, "d"=>42}

a = "a" 
b = "b".freeze 
h = { a => 100, b => 200 } 
puts (h.key(100).equal? a).inspect #=> false 
puts (h.key(200).equal? b).inspect #=> true

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300 } 
puts h.to_a.inspect #=> [["c", 300], ["a", 100], ["d", 400]]

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300 } 
puts h.to_s #=> {"c"=>300, "a"=>100, "d"=>400}

h1 = { "a" => 100, "b" => 200 } 
h2 = { "b" => 254, "c" => 300 } 
puts h1.update(h2).inspect #=> {"a"=>100, "b"=>254, "c"=>300} 
h1 = { "a" => 100, "b" => 200 } 
h2 = { "b" => 254, "c" => 300 } 
puts h1.update(h2) { |key, v1, v2| v1 }.inspect #=> {"a"=>100, "b"=>200, "c"=>300}

puts h.value?(100).inspect #=> true 
puts h.value?(999).inspect #=> false

puts h.values.inspect #=> [100, 200, 300]

h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" } 
puts h.values_at("cow", "cat").inspect #=> ["bovine", "feline"]

---