Iterating over hash elements

Iteration over hash elements isn’t something you see very often, because the main purpose of hash data structure is to add and access elements by a key. However, it’s always good to know and have understanding about how to iterate over elements. We already know how to iterate over arrays:

arr.each do |element|
  # do something with element
end 

Iteration over key-value pairs looks similar:

hh = {
  soccer_ball: 410,
  tennis_ball: 58,
  golf_ball: 45
}

hh.each do |k, v|
  puts "Weight of #{k} is #{v} grams"
end

Result:

Weight of soccer_ball is 410 grams
Weight of tennis_ball is 58 grams
Weight of golf_ball is 45 grams

Variables “k” and “v” represent key and value of this particular iteration. You can omit value if you don’t need it, or just replace “v” with a string starting with “_” (underscore), or just with a single underscore. It’s not a Ruby syntax, but naming conventions everyone understands - if you don’t need something, use underscore prefix to show your intention:

hh = {
  soccer_ball: 410,
  tennis_ball: 58,
  golf_ball: 45
}

hh.each do |k, _|
  puts "Warehouse has #{k}"
end

Code above can also be rewritten by using “each_key” method of a Hash class.

Exercise Given the following data:

data = {
  soccer_ball: { name: 'Soccer ball', weight: 410, qty: 5 },
  tennis_ball: { name: 'Tennis ball', weight: 58, qty: 10 },
  golf_ball: { name: 'Golf ball', weight: 45, qty: 15 }
}

Write a program that prints:

Warehouse availability:
Soccer ball, weight 410 grams, quantity: 5 items
Tennis ball, weight 58 grams, quantity: 10 items
Golf ball, weight 45 grams, quantity: 15 items