Add Hash#invert

mrbgems/mruby-hash-ext/mrblib/hash.rb

@@ -120,4 +120,21 @@ class Hash
   def flatten(level=1)
     self.to_a.flatten(level)
   end
+
+  ##
+  #  call-seq:
+  #     hsh.invert -> new_hash
+  #
+  #  Returns a new hash created by using <i>hsh</i>'s values as keys, and
+  #  the keys as values.
+  #
+  #     h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
+  #     h.invert   #=> {0=>"a", 100=>"m", 200=>"d", 300=>"y"}
+  #
+
+  def invert
+    h = Hash.new
+    self.each {|k, v| h[v] = k }
+    h
+  end
 end

mrbgems/mruby-hash-ext/test/hash.rb

@@ -82,3 +82,16 @@ assert("Hash#flatten") do
   assert_equal [1, "one", 2, 2, "two", 3, 3, ["three"]], a.flatten(2)
   assert_equal [1, "one", 2, 2, "two", 3, 3, "three"], a.flatten(3)
 end
+
+assert("Hash#invert") do
+  h = { 1 => 'one', 2 => 'two', 3 => 'three',
+        true => 'true', nil => 'nil' }.invert
+  assert_equal 1, h['one']
+  assert_equal true, h['true']
+  assert_equal nil, h['nil']
+
+  h = { 'a' => 1, 'b' => 2, 'c' => 1 }.invert
+  assert_equal(2, h.length)
+  assert_include(%w[a c], h[1])
+  assert_equal('b', h[2])
+end