Calculate the sum of objects for each property of a unique object in Ruby

I helped with an answer in this question and it raised a question of my own.

• Pie
  
  is an object that has an array pieces
  
  of PiePiece
  
  objects.
• Everyone PiePiece
  
  has an attributeflavor
  
  

How to create a hash that looks like this:

# flavor => number of pieces
{
  :cherry => 3
  :apple => 1
  :strawberry => 2
}

      

        
        
        
      

    

It works, but I think it could be improved

def inventory
  hash = {}
  pieces.each do |p|
    hash[p.flavor] ||= 0
    hash[p.flavor] += 1
  end
  hash
end

      

        
        
        
      

    

Any ideas?