From: Stefano Crocco <stefano.crocco@...>
Date: 2007-05-19T05:59:40+09:00
Subject: Re: multimimensional arrays - i am not getting it..

Alle venerd狸 18 maggio 2007, Sergio Ruiz ha scritto:
> let me just give a blip of what i am getting...
>
> >> a = Array.new(3,[])
>
> => [[], [], []]
>
> >> a[2] << "check"
>
> => ["check"]
>
> >> a
>
> => [["check"], ["check"], ["check"]]
>
> this is totally not what i am expecting..
>
> what i am expecting is:
>
> [[],[],[["check"]]]
>
> as in..
>
> the 2 element should have the "check" string dropped into the next
> available position..
>
> how would i go about setting that (or any other) element only?
>
> thanks!

Look at the documentation for Array.new (ri Array.new). Array.new(n, obj) 
creates an array with n entries, all containing the same object, obj. You can 
see this comparing the entries' object_id, or using equal?: a[0].equal?(a[1]) 
=> true. Since all entries contain the same object, when you modify it, the 
change shows everywhere in the array.

To fill the array with *different* empty arrays, you need to use the form of 
Array.new which takes a block:

Array.new(3){[]}

In this form, the block is called for each index, with the index as argument 
(you can omit it here because you don't need it). The result of the block is 
stored in the corresponding entry. The point is that each time the block is 
called, a *new* empty array is created and stored in the returned array. This 
time, a[0].equal?(a[1]) gives false.

I hope this helps

Stefano