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Iterating Over a Hash
CodeExpectedActual
hash = { 1 => 'one', [1,2] => 'two', 'three' => 'three' }
hash.each_pair { |key, value| puts "#{key.inspect} maps to #{value}"}
 
[1, 2] maps to two
"three" maps to three
1 maps to one
 
[1, 2] maps to two
"three" maps to three
1 maps to one
 
active_toggles = { 'super' => true, 'meta' => true, 'hyper' => true }
active_toggles.each_key { |active| puts active }
 
hyper
meta
super
 
hyper
meta
super
 
favorite_colors = { 'Alice' => :red, 'Bob' => :violet, 'Mallory' => :blue,
                    'Carol' => :blue, 'Dave' => :violet }
summary = Hash.new(0)
favorite_colors.each_value { |x| summary[x] += 1 }
summary
 {:red=>1, :violet=>2, :blue=>2} {:red=>1, :violet=>2, :blue=>2} 
hash = {}
1.upto(10) { |x| hash[x] = x * x }
hash.has_value? 49
 true true 
hash.has_value? 81
 true true 
hash.has_value? 50
 false false 
1.upto(100) { |x| hash[x] = true }
hash.keys { |k| hash[k * 2] = true }
 
RuntimeError: hash modified during iteration
 






hash = {1 => 2, 2 => 2, 3 => 10}
hash.keys

[1, 2, 3]
[1, 2, 3]





hash.values

[2, 2, 10]
[2, 2, 10]





hash.to_a

[[1, 2], [2, 2], [3, 10]]
[[1, 2], [2, 2], [3, 10]]





extensions = { 'Alice' => '104', 'Carol' => '210', 'Bob' => '110' }
extensions.keys.sort.each do |k| 
  puts "#{k} can be reached at extension ##{extensions[k]}"
end


Alice can be reached at extension #104
Bob can be reached at extension #110
Carol can be reached at extension #210


Alice can be reached at extension #104
Bob can be reached at extension #110
Carol can be reached at extension #210






to_do = { 'Clean car' => 5, 'Take kangaroo to vet' => 3, 
          'Realign plasma conduit' => 3 }
to_do.sort_by { |task, priority| [priority, task] }.each { |k,v| puts k }


Realign plasma conduit
Take kangaroo to vet
Clean car


Realign plasma conduit
Take kangaroo to vet
Clean car






transform_results = { 4 => 8, 9 => 9, 10 => 6, 2 => 7, 6 => 5 }
by_size_of_difference = transform_results.sort_by { |x, y| (x-y).abs }
by_size_of_difference.each { |x, y| puts "f(#{x})=#{y}: difference #{y-x}" }


f(9)=9: difference 0
f(6)=5: difference -1
f(10)=6: difference -4
f(4)=8: difference 4
f(2)=7: difference 5


f(9)=9: difference 0
f(6)=5: difference -1
f(10)=6: difference -4
f(4)=8: difference 4
f(2)=7: difference 5