Sorting an array of ActiveRecord objects on multiple attributes

 def sort(arr, crit, i)
    final = []
    arr = arr.sort_by {|a| a.send(crit[i])}
    hash = arr.slice_into_groups(crit[i])
    sorted_keys = hash.sort_by {|k, v| k}.gimme_firsts
    if i < crit.size - 1
      sorted_keys.each do |key|
        final << sort(hash[key], crit, i+1)
      end
    else
      final = arr
    end
    return final.flatten
  end
   
  class Array
  
  def slice_into_groups(crit)
    hash = {}
    self.each do |a|
      hash[a.send(crit)] = [] if hash[a.send(crit)].blank?
      hash[a.send(crit)] << a
    end
    hash
  end

  def gimme_firsts
    self.collect{|a| a.first}
  end

class ArrayTest < Test::Unit::TestCase
  def test_slice_into_groups
    objects = Model.find(:all)
    assert_not_nil objects.size
    old_size = objects.size

    grouped_objects = objects.slice_into_groups('attribute')

    sum = 0
    grouped_objects.each do |k, v|
      sum += v.size
      v.each do |obj|
        assert_equal k, obj.attribute
      end
    end
    assert_equal old_size, sum
  end

  def test_gimme_firsts
    assert_equal [1, 2, 3, 4, 5, 6, 7], [[1, 2, 3],[2, 2, 3],[3, 2, 3],[4, 2, 3],[5, 2, 3],[6, 2, 3],[7, 2, 3]].gimme_firsts
  end
end