From: dblack@...
Date: 2007-03-01T11:57:10+09:00
Subject: Re: Array comparison.. why does this work.

Hi --

On Thu, 1 Mar 2007, Jean Nibee wrote:

> How does Ruby do Array comparision?

One element at a time.

> [code]
> old_inventory = [ 'a', 'b', 'd' ]
> new_inventory = [ 'a','e', 'c' ]
>
> puts "The following files have been added: "
> puts new_inventory - old_inventory
> puts ""
> puts "The following files have been deleted: "
> puts old_inventory - new_inventory
> [/code]
>
> Notice the output is correct so it's not a case of element 0's being
> compared in each array.
>
> So...
>
> Does Ruby sort arrays in memory first? or is a scan done 1 element at a
> time?

You're not doing comparison, though; you're doing subtraction.
Subtraction doesn't depend on order.  You can think of it as
"without":

   [1,2,3] - [1]    => [2,3]  # [1,2,3] without 1
   [1,2,3,1] - [1]  => [2,3]  # [1,2,3,1] without 1
   [1,2,3] - [2]    => [1,3]  # [1,2,3] without 2

etc.


David

-- 
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