Ruby Hash with duplicate keys?

问题:

Is it possible to create a hash in Ruby that allows duplicate keys?

I'm working in Ruby 1.9.2.

回答1:

This would kinda defeat the purpose of a hash, wouldn't it?

If you want a key to point to multiple elements, make it point to an array:

h = Hash.new { |h,k| h[k] = [] }
h[:foo] << :bar
h #=> {:foo=>[:bar]}
h[:foo] << :baz
h #=> {:foo=>[:bar, :baz]}

回答2:

Two ways of achieving duplicate keys in a hash:

h1 = {}
h1.compare_by_identity
h1["a"] = 1
h1["a"] = 2
p h1 # => {"a"=>1, "a"=>2}


h2 = {}
a1 = [1,2,3]
a2 = [1,2]
h2[a1] = 1
h2[a2] = 2
a2 << 3 
p h2 # => {[1, 2, 3]=>1, [1, 2, 3]=>2}