Collections

Hash Iteration

A hash stores named values and can be iterated to compute a total.

hash iteration `each` visits every key and value pair in a hash.

Hash Iteration

lookup
hash_iteration.rb
Replay: real traced execution (multi-file project)
prices = { apple: 2, banana: 3, pear: 4 }
lookup = :pear

total = 0
prices.each do |name, price|
  total += price
  puts "#{name}=#{price}"
end

found = prices[lookup] || 0

puts "total=#{total}"
puts "lookup=#{lookup}"
puts "found=#{found}"

prices = { apple: 2, banana: 3, pear: 4 }
lookup = :apple

total = 0
prices.each do |name, price|
  total += price
  puts "#{name}=#{price}"
end

found = prices[lookup] || 0

puts "total=#{total}"
puts "lookup=#{lookup}"
puts "found=#{found}"

prices = { apple: 2, banana: 3, pear: 4 }
lookup = :orange

total = 0
prices.each do |name, price|
  total += price
  puts "#{name}=#{price}"
end

found = prices[lookup] || 0

puts "total=#{total}"
puts "lookup=#{lookup}"
puts "found=#{found}"

  1. prices ← {:apple=>2, :banana=>3, :pear=>4}, lookup ← pear, total ← 0

    1prices→ {:apple=>2, :banana=>3, :pear=>4} = { apple: 2, banana: 3, pear: 4 }2lookup→ pear = :pear  #@lookup=:apple, :orange34total→ 0 = 05prices{:apple=>2, :banana=>3, :pear=>4}.each do |name, price|6  total += price7  puts "#{name}=#{price}"8end

  2. total ← 2

    pass 1 of 3
    4total = 05prices.each do |nameapple, price2|6  total→ 2 += price27  puts "#{nameapple}=#{price2}"8end
    outputapple=2
    All 3 passes — pass 1 is the card above
    passnamepricepricestotal
    1apple2—0 → 2
    2banana3—2 → 5
    3pear4{:apple=>2, :banana=>3, :pear=>4}5 → 9

  3. found ← 4

    10found→ 4 = prices[lookup]4 || 01112puts "total=#{total9}"13puts "lookup=#{lookuppear}"14puts "found=#{found4}"
    outputtotal=9
lookup=pear
found=4

  1. prices ← {:apple=>2, :banana=>3, :pear=>4}, lookup ← apple, total ← 0

    1prices→ {:apple=>2, :banana=>3, :pear=>4} = { apple: 2, banana: 3, pear: 4 }2lookup→ apple = :apple34total→ 0 = 05prices{:apple=>2, :banana=>3, :pear=>4}.each do |name, price|6  total += price7  puts "#{name}=#{price}"8end

  2. total ← 2

    pass 1 of 3
    4total = 05prices.each do |nameapple, price2|6  total→ 2 += price27  puts "#{nameapple}=#{price2}"8end
    outputapple=2
    All 3 passes — pass 1 is the card above
    passnamepricepricestotal
    1apple2—0 → 2
    2banana3—2 → 5
    3pear4{:apple=>2, :banana=>3, :pear=>4}5 → 9

  3. found ← 2

    10found→ 2 = prices[lookup]2 || 01112puts "total=#{total9}"13puts "lookup=#{lookupapple}"14puts "found=#{found2}"
    outputtotal=9
lookup=apple
found=2

  1. prices ← {:apple=>2, :banana=>3, :pear=>4}, lookup ← orange, total ← 0

    1prices→ {:apple=>2, :banana=>3, :pear=>4} = { apple: 2, banana: 3, pear: 4 }2lookup→ orange = :orange34total→ 0 = 05prices{:apple=>2, :banana=>3, :pear=>4}.each do |name, price|6  total += price7  puts "#{name}=#{price}"8end

  2. total ← 2

    pass 1 of 3
    4total = 05prices.each do |nameapple, price2|6  total→ 2 += price27  puts "#{nameapple}=#{price2}"8end
    outputapple=2
    All 3 passes — pass 1 is the card above
    passnamepricepricestotal
    1apple2—0 → 2
    2banana3—2 → 5
    3pear4{:apple=>2, :banana=>3, :pear=>4}5 → 9

  3. found ← 0

    10found→ 0 = prices[lookup](empty) || 01112puts "total=#{total9}"13puts "lookup=#{lookuporange}"14puts "found=#{found0}"
    outputtotal=9
lookup=orange
found=0