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 can be done fairly succinctly using each_with_object.

array.each_with_object({}) { |(k, v), h| h[k] = (h[k] || []) + [v] }

Demonstrating in irb:

irb(main):002:0> array = [[:a,:b],[:a,:c],[:c,:b]]
=> [[:a, :b], [:a, :c], [:c, :b]]
irb(main):003:0> array.each_with_object({}) { |(k, v), h| h[k] = (h[k] || []) + [v] }
=> {:a=>[:b, :c], :c=>[:b]}