From: Shashank Date <sdate@...>
Date: 2002-12-09T07:23:22+09:00
Subject: Re: multi-dimension array


"Shannon Fang" <xrfang@hotmail.com> wrote in message
news:20021208193614.A604.XRFANG@hotmail.com...
> Hi there,
>
> I am a little confused about multi-dimension array definition in ruby.

It's OK ... it is confusing in the beginning to most of us (especially if
coming from C background)

> I tried the following
> a=Array.new(3,Array.new(2,Array.new))
> p a
>
> out put is:
> [[[ ], [ ]], [[ ], [ ]], [[ ], [ ]]]

Correct ! It did what you asked it do ... reading Array.new from inside out:
First create an Array object with no elements (like [])
Then use it as the initial value of another Array object with 2 elements.
Then use this as the initial value of the final Array object with 3
elements.

Hence:

 [[[ ], [ ]], [[ ], [ ]], [[ ], [ ]]]

Moreover, if you tried:

a[0][0][0] = 1
p a

you would now get

[[[1], [1]], [[1], [1]], [[1], [1]]]

Surprised, eh ?

> What I need is a 2 dimesional array a, with the following elements
> a[0][0]
> a[0][1]
> a[1][0]
> a[1][1]
> a[2][0]
> a[2][1]

Then you should try :

a = Array.new(2,Array.new(2,0))
p a

[[0,0],[0,0],[0,0]]

But then again,

a[0][0] = 1
p a

will give you :

[[1, 0], [1, 0]]

So the other approach is:

arr = Array.new(2)
arr.each_index { |i|
    r = Array.new(2)
    r.each_index { |j|
        r[j] = 0
    }
    arr[i] = r
}
p arr

will give you:

[[0,0],[0,0],[0,0]]

Now if you do:

arr[0][0] = 1
p arr

you will get:

[[1,0],[0,0],[0,0]]

Is that what you wanted ?

HTH,
-- shanko