ruby - How do I merge two hashes into a hash of arrays? -

http://codepad.org/wmyzqlis

i'd merge these 2 arrays:

a = { :a => 'a', :b => 'b', :d => 'd' } b = { :a => '1', :b => 'b', :c => 'c' } 

into hash looks this:

{:a => ["a", "1"], :b => ["b", "b"], :c => [nil, "c"], :d => ["d", nil] } 

this doesn't work:

p a.merge(b) { |k, v1, v2| [v1, v2] }    # {:c=>"c", :a=>["a", "1"], :b=>["b", "b"], :d=>"d"} 

it's because hash#merge call block duplicate keys.

---

a = { :a => 'a', :b => 'b', :d => 'd' } b = { :a => '1', :b => 'b', :c => 'c' }  hash[(a.keys|b.keys).map { |key|   [key, [a.fetch(key, nil), b.fetch(key, nil)]] }] # => {:a=>["a", "1"], :b=>["b", "b"], :d=>["d", nil], :c=>[nil, "c"]}  # in ruby 2.1+ (a.keys|b.keys).map { |key|   [key, [a.fetch(key, nil), b.fetch(key, nil)]] }.to_h