From: Jeff Nyman <jeffnyman_nospam@..._gmail.com>
Date: 2006-10-09T20:20:17+09:00
Subject: Removing Duplicate Objects from Object List

Greetings all.

Does anyone have a good idea of how to write a loop that checks if two 
objects are equal? By "equal" here I refer to the 'eql' method, to test if 
the objects have the same value.

I have set of Rule objects that will be stored in a RuleList object. I know 
how to cycle through the RuleList. I'm just doing this:

$ruleList.selection.each { |rule|
  ...
}

The problem is that I need to go through each rule and check if it is equal 
to *any* of the other rules that are in the list. If a duplicate is found, 
one of the duplicate rules should be removed.

Every solution I've tried has ended up either removing objects incorrectly 
or not finding the duplicates in the first place.

Here's an example of some Rule objects:

<Tendent::Rule:0x2d5f7a8 @filter="first after 202G_OrdAdd", 
@value="203G_OrdUpdateFirst", @point="203G_OrdUpdateFirst">
<Tendent::Rule:0x2d5f71c @filter="last", @value="203G_OrdUpdateLast", 
@point="203G_OrdUpdateLast">
<Tendent::Rule:0x2d5f6a4 @filter="first after 202G_OrdAdd", 
@value="203G_OrdUpdateFirst", @point="203G_OrdUpdateFirst">
<Tendent::Rule:0x2d5f62c @filter="last", @value="203G_OrdUpdateLast", 
@point="203G_OrdUpdateLast">

Here is what they look like as strings:

203G_OrdUpdateFirst, first after 202G_OrdAdd, 203G_OrdUpdateFirst
203G_OrdUpdateLast, last, 203G_OrdUpdateLast
203G_OrdUpdateFirst, first after 202G_OrdAdd, 203G_OrdUpdateFirst
203G_OrdUpdateLast, last, 203G_OrdUpdateLast

So as you can see, I have four rules, but actually only two are unique. 
(That just happens to be the case here. In other cases, perhaps there will 
be six rules, and two will be unique.)

Can anyone see an efficient way to do this?

Is it better to just convert these into an array? I know the Array class has 
the 'uniq' method. The problem is that I would still need the rules to then 
be objects as well. In other words, even if I put all the objects in an 
array and modify the array, I would need to reflect the changes in the 
object list itself, such that the duplicate objects no longer exist.

- Jeff