From: Ryan Davis <ryand-ruby@...>
Date: 2010-02-04T10:53:21+09:00
Subject: Re: [Chris Pine] Chapter 7 - Sorting Arrays without .sort


On Feb 3, 2010, at 15:33 , Siep Korteling wrote:

> Don't worry about the size of the array, ruby does take care of that.
> Don't worry about the order, strings know if they are "bigger" than 
> another string.
> Aldric Giacomoni adheres to the principle: go find it out for yourself, 
> and he's right; that's the way to go. But if you are like me, a relative 
> simple concept like recursion takes a long time to sink in, and a did 
> not find (in my time) any resources which explained it in terms I 
> understood. Here's my take at explaining (in code):

I'd disagree in principal with Aldric's advice. For starters, your original instructions say:

"Let's write a program which asks us to type in as many words as we want
(one word per line, continuing until we just press Enter on an empty
line), and which then repeats the words back to us in alphabetical
order.
Try writing the above program without using the sort method."

Start smaller. First write the program using Array#sort. So:

+ take user input until an empty line
+ add each user input to an array
+ print it back out sorted (for starters, using Array#sort).

Once you have that down, THEN work on replacing the call to Array#sort with Array#mysort (or whatever).

> p recursive_sort!(["xenophobia", "foo","baz", "aardvark","bezerk"])

Make this easier by doing the following:

if $0 == __FILE__ then
  require 'test/unit'

  class TestSort < Test::Unit::TestCase
    def test_mysort
      input = ["xenophobia", "foo","baz", "aardvark","bezerk"]
      expect = %w(aardvark baz bezerk foo xenophobia) # prettier, no?

      assert_equal expect, input.mysort
    end
  end
end

add that to the bottom of your sort algorithm, or in a separate file (exclude the surrounding if, and be sure to require your sort algorithm). When you run it, you'll get a failure... now make it pass.