Count occurrences

You can use Enumerable#tally to get a hash of element counts

["apple", "banana", "apple", "orange", "banana"].tally
=> {"apple"=>2, "banana"=>2, "orange"=>1}

We can even make it work for nested arrays

outfits = [
  ["Red Shirt"],
  ["Red Shirt", "Blue Pants"],
  ["Blue Pants"],
  ["Red Shirt"],
]

outfits.tally.map { |k, v| [*k, v] }
=> 
[
  ["Red Shirt", 2],
  ["Red Shirt", "Blue Pants", 1],
  ["Blue Pants", 1]
]