Convert array of 2-element arrays into a hash, where duplicate keys append additional values

Question

For example

Given an array:

array = [[:a,:b],[:a,:c],[:c,:b]]

Return the following hash:

hash = { :a => [:b,:c         


        

Answer 1

This kind of operations is very common in our project, so we added to_group_h to Enumerable. We can use it like:

[[:x, 1], [:x, 2], [:y, 3]].to_h
# => { x: 2, y: 3 }

[[:x, 1], [:x, 2], [:y, 3]].to_group_h
# => { x: [1, 2], y: [3] }

The following is the implementation of Enumerable#to_group_h:

module Enumerable
  if method_defined?(:to_group_h)
    warn 'Enumerable#to_group_h is defined'
  else
    def to_group_h
      hash = {}
      each do |key, value|
        hash[key] ||= []
        hash[key] << value
      end
      return hash
    end
  end
end