From: Stefano Crocco <stefano.crocco@...>
Date: 2007-01-30T02:18:31+09:00
Subject: Re: classification

Alle luned� 29 gennaio 2007, Josselin ha scritto:
> I have to classify a bunch of products into 4 boxes, according to the
> value of one of their attribute (product.code , an integer between 0
> and 4)
>
> I wrote that but it's seems wrong  :
>
> box[0] = box[1] = box[2] = box[3] = []
>
> for product in products
>  tag = Tag.new(product.title, product.price)
>  box[ product.code�] << tag
> end
>
> then I'll reuse each box[] for further processing...
>
> what's wrong ?
>
> tfyl
>
> joss

The problem is that writing something like

a = b = c = []

will store the same array in all the variables. If you use the object_id 
methods on the four elements of box, you'll see that the returned value is 
the same. This means that modifiying, for instance box[0] will also modify 
box[1], box[2] and box[3], because they all contain the same object. You 
should replace the line

box[0] = box[1] = box[2] = box[3] = []

with, for example,

box=Array.new(4){[]}

This will create a new Array with four elements, each of which is a different 
Array. Note that writing box=Array.new(4,[]) will produce the same (wrong) 
result as your code.

I hope this helps

Stefano