Add Hash#keep_if

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

@@ -137,4 +137,27 @@ class Hash
     self.each {|k, v| h[v] = k }
     h
   end
+
+  ##
+  #  call-seq:
+  #     hsh.keep_if {| key, value | block }  -> hsh
+  #     hsh.keep_if                          -> an_enumerator
+  #
+  #  Deletes every key-value pair from <i>hsh</i> for which <i>block</i>
+  #  evaluates to false.
+  #
+  #  If no block is given, an enumerator is returned instead.
+  #
+
+  def keep_if(&block)
+    return to_enum :keep_if unless block_given?
+
+    keys = []
+    self.each do |k, v|
+      unless block.call([k, v])
+        self.delete(k)
+      end
+    end
+    self
+  end
 end

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

@@ -95,3 +95,10 @@ assert("Hash#invert") do
   assert_include(%w[a c], h[1])
   assert_equal('b', h[2])
 end
+
+assert("Hash#keep_if") do
+  h = { 1 => 2, 3 => 4, 5 => 6 }
+  assert_equal({3=>4,5=>6}, h.keep_if {|k, v| k + v >= 7 })
+  h = { 1 => 2, 3 => 4, 5 => 6 }
+  assert_equal({ 1 => 2, 3=> 4, 5 =>6} , h.keep_if { true })
+end