hash_recursive_merge.rb

# 
# = Hash Recursive Merge
# 
# Merges a Ruby Hash recursively, Also known as deep merge.
# Recursive version of Hash#merge and Hash#merge!.
# 
# Category::    Ruby
# Package::     Hash
# Author::      Simone Carletti <weppos@weppos.net>
# Copyright::   2007-2008 The Authors
# License::     MIT License
# Link::        http://www.simonecarletti.com/
# Source::      http://gist.github.com/gists/6391/
#
module HashRecursiveMerge

  #
  # Recursive version of Hash#merge!
  # 
  # Adds the contents of +other_hash+ to +hsh+, 
  # merging entries in +hsh+ with duplicate keys with those from +other_hash+.
  # 
  # Compared with Hash#merge!, this method supports nested hashes.
  # When both +hsh+ and +other_hash+ contains an entry with the same key,
  # it merges and returns the values from both arrays.
  # 
  #    h1 = {"a" => 100, "b" => 200, "c" => {"c1" => 12, "c2" => 14}}
  #    h2 = {"b" => 254, "c" => {"c1" => 16, "c3" => 94}}
  #    h1.rmerge!(h2)   #=> {"a" => 100, "b" => 254, "c" => {"c1" => 16, "c2" => 14, "c3" => 94}}
  #    
  # Simply using Hash#merge! would return
  # 
  #    h1.merge!(h2)    #=> {"a" => 100, "b" = >254, "c" => {"c1" => 16, "c3" => 94}}
  # 
  def rmerge!(other_hash)
    merge!(other_hash) do |key, oldval, newval|
      oldval.class == self.class ? oldval.rmerge!(newval) : newval
    end
  end

  #
  # Recursive version of Hash#merge
  # 
  # Compared with Hash#merge!, this method supports nested hashes.
  # When both +hsh+ and +other_hash+ contains an entry with the same key,
  # it merges and returns the values from both arrays.
  # 
  # Compared with Hash#merge, this method provides a different approch
  # for merging nasted hashes.
  # If the value of a given key is an Hash and both +other_hash+ abd +hsh
  # includes the same key, the value is merged instead replaced with
  # +other_hash+ value.
  # 
  #    h1 = {"a" => 100, "b" => 200, "c" => {"c1" => 12, "c2" => 14}}
  #    h2 = {"b" => 254, "c" => {"c1" => 16, "c3" => 94}}
  #    h1.rmerge(h2)    #=> {"a" => 100, "b" => 254, "c" => {"c1" => 16, "c2" => 14, "c3" => 94}}
  #    
  # Simply using Hash#merge would return
  # 
  #    h1.merge(h2)     #=> {"a" => 100, "b" = >254, "c" => {"c1" => 16, "c3" => 94}}
  # 
  def rmerge(other_hash)
    r = {}
    merge(other_hash) do |key, oldval, newval|
      r[key] = oldval.class == self.class ? oldval.rmerge(newval) : newval
    end
  end

end


class Hash
  include HashRecursiveMerge
end

hash_recursive_merge_spec.rb

require "spec_helper"

describe Hash do

  before(:each) do
    @simple_h1 = { 'a' => 100, 'b' => 200 }
    @simple_h2 = {             'b' => 254, 'c' => 300 }
    @nested_h1 = { 'a' => 100, 'b' => 200, 'c' => { 'c1' => 12, 'c2' => 14 }}
    @nested_h2 = {             'b' => 254, 'c' => { 'c1' => 16,            'c3' => 94 }}
  end

  describe "#rmerge" do
    it "should merge simple hashes" do
      @simple_h1.rmerge(@simple_h2).should == { 'a' => 100, 'b' => 254, 'c' => 300 }
      @simple_h2.rmerge(@simple_h1).should == { 'a' => 100, 'b' => 200, 'c' => 300 }
    end

    it "should merge nested hashes" do
      @nested_h1.rmerge(@nested_h2).should ==
      { 'a' => 100, 'b' => 254, 'c' => { 'c1' => 16, 'c2' => 14, 'c3' => 94 }}

      @nested_h2.rmerge(@nested_h1).should ==
      { 'a' => 100, 'b' => 200, 'c' => { 'c1' => 12, 'c2' => 14, 'c3' => 94 }}
    end
  end

  describe "#rmerge!" do
    it "should merge simple hashes and modify the receiver" do
      @simple_h1.rmerge!(@simple_h2)
      @simple_h1.should == { 'a' => 100, 'b' => 254, 'c' => 300 }

      @simple_h1 = { 'a' => 100, 'b' => 200 }
      @simple_h2.rmerge!(@simple_h1)
      @simple_h2.should == { 'a' => 100, 'b' => 200, 'c' => 300 }
    end

    it "should merge nested hashes and modify the receiver" do
      @nested_h1.rmerge!(@nested_h2)
      @nested_h1.should ==
      { 'a' => 100, 'b' => 254, 'c' => { 'c1' => 16, 'c2' => 14, 'c3' => 94 }}

      @nested_h1 = { 'a' => 100, 'b' => 200, 'c' => { 'c1' => 12, 'c2' => 14 }}
      @nested_h2.rmerge!(@nested_h1)
      @nested_h2.should ==
      { 'a' => 100, 'b' => 200, 'c' => { "c1" => 12, "c2" => 14, "c3" => 94 }}
    end
  end

end

hash_recursive_merge_test.rb

require 'test/unit'
require 'hash_recursive_merge'


class HashRecursiveMergeTest < Test::Unit::TestCase
  
  def test_rmerge_should_be_available_to_any_instance_of_hash
    assert(Hash.new.public_methods.include?('rmerge'))
  end
  
  def test_rmerge_bang_should_be_available_to_any_instance_of_hash
    assert(Hash.new.public_methods.include?('rmerge!'))
  end
  
  def test_rmerge_should_merge_simple_hashes
    h1 = { 'a' => 100, 'b' => 200 }
    h2 = { 'b' => 254, 'c' => 300 }
    assert_equal({ 'a' => 100, 'b' => 254, 'c' => 300 }, h1.rmerge(h2))
    assert_equal({ 'a' => 100, 'b' => 200, 'c' => 300 }, h2.rmerge(h1))
  end
  
  def test_rmerge_should_merge_nested_hashes
    h1 = { 'a' => 100, 'b' => 200, "c" => { "c1" => 12, "c2" => 14 }}
    h2 = { 'b' => 254, "c" => { "c1" => 16, "c3" => 94 }}
    assert_equal({ 'a' => 100, 'b' => 254, 'c' => { "c1" => 16, "c2" => 14, "c3" => 94 }}, h1.rmerge(h2))
    assert_equal({ 'a' => 100, 'b' => 200, 'c' => { "c1" => 12, "c2" => 14, "c3" => 94 }}, h2.rmerge(h1))
  end
  
  def test_rmerge_bang_should_merge_simple_hashes
    h1 = { 'a' => 100, 'b' => 200 }
    h2 = { 'b' => 254, 'c' => 300 }
    h1.rmerge!(h2)
    assert_equal({ 'a' => 100, 'b' => 254, 'c' => 300 }, h1)

    h1 = { 'a' => 100, 'b' => 200 }
    h2 = { 'b' => 254, 'c' => 300 }
    h2.rmerge!(h1)
    assert_equal({ 'a' => 100, 'b' => 200, 'c' => 300 }, h2)
  end
  
  def test_rmerge_should_merge_nested_hashes
    h1 = { 'a' => 100, 'b' => 200, "c" => { "c1" => 12, "c2" => 14 }}
    h2 = { 'b' => 254, "c" => { "c1" => 16, "c3" => 94 }}
    h1.rmerge!(h2)
    assert_equal({ 'a' => 100, 'b' => 254, 'c' => { "c1" => 16, "c2" => 14, "c3" => 94 }}, h1)

    h1 = { 'a' => 100, 'b' => 200, "c" => { "c1" => 12, "c2" => 14 }}
    h2 = { 'b' => 254, "c" => { "c1" => 16, "c3" => 94 }}
    h2.rmerge!(h1)
    assert_equal({ 'a' => 100, 'b' => 200, 'c' => { "c1" => 12, "c2" => 14, "c3" => 94 }}, h2)
  end
  
end