From: Michael W Ryder <data@...>
Date: 2010-02-04T13:22:15+09:00
Subject: Re: [Chris Pine] Chapter 7 - Sorting Arrays without .sort

On 2/3/2010 5:53 PM, Ryan Davis wrote:
>
> 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).
>

Wouldn't it be easier to just sort the data as it is input, a simple 
insert sort?


>> 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.