Ruby Array to Hash

class Array
  def to_hashkeys(&block)
    Hash[*self.collect { |v|
      [v, block.call(v)]
    }.flatten]
  end
 
  def to_hashvalues(&block)
    Hash[*self.collect { |v|
      [block.call(v), v]
    }.flatten]
  end
end

>> a = ["a", "b", "c"]
>> a.to_hashvalues {|v| a.index(v)}
=> {0=>"a", 1=>"b", 2=>"c"}

class Array
  def to_hash(other)
    Hash[ *(0...self.size()).inject([]) { |arr, ix| arr.push(self[ix], other[ix]) } ]
  end
end
%W{ a b c }.to_hash( %W{ 1 2 3 } )
 
#=> {"a"=>"1", "b"=>"2", "c"=>"3"}

a = [1, 2, 3].collect { |v| [v, v*2] }      # => [ [1, 2], [2, 4], [3, 6] ]
Hash[*a.flatten]                            # => {1=>2, 2=>4, 3=>6}

a = [1, 2, 3].collect { |v| [v, v*2] }      # => [ [1, 2], [2, 4], [3, 6] ]
Hash[a]                                     # => {1=>2, 2=>4, 3=>6}

h = { :a => 1, :b => 2}   # Start with a hash
a = h.to_a                # => [[:b,2], [:a,1]]: associative array
a.assoc(:a)               # => [:a,1]: subarray for key :a
a.assoc(:b).last          # => 2: value for key :b
a.rassoc(1)               # => [:a,1]: subarray for value 1
a.rassoc(2).first         # => :b: key for value 2
a.assoc(:c)               # => nil
a.transpose               # => [[:a, :b], [1, 2]]: swap rows and cols