pizzas.rb

require 'open-uri'
require 'json'

p = JSON.parse(URI.parse('http://files.olo.com/pizzas.json').read).map { |p| p['toppings'].sort.join(', ') }.flatten
puts p.uniq.map { |c| [c, p.count(c)]}.sort { |a,b| b[1] <=> a[1] }[0...20].map.with_index { |t,i| "#{i+1}. #{t[0]}: #{t[1]}" }.join("\n")

1. pepperoni: 4616
2. mozzarella cheese: 1014
3. four cheese: 956
4. bacon: 732
5. beef: 623
6. sausage: 402
7. italian sausage: 361
8. chicken: 229
9. four cheese, pepperoni: 203
10. ham: 165
11. mushrooms: 159
12. mozzarella cheese, pepperoni: 155
13. beef, pepperoni: 122
14. bacon, pepperoni: 121
15. black olives: 117
16. alredo sauce: 101
17. pepperoni, sausage: 96
18. cheddar cheese: 95
19. italian sausage, pepperoni: 85
20. pineapple: 79