From: Joe Seeley <joiey.seeley@...>
Date: 2006-05-16T22:34:43+09:00
Subject: Re: 2 dimensional arrays

Timothy Hunter wrote:
> On May 15, 2006, at 5:06 PM, Joe Seeley wrote:
> 
>> The 2 dimensional array or table structure is extremely common, but I
>> don't see a simple/standard way to implement this in Ruby.  Is  
>> there an
>> easy way to do this?
>>
>> -- 
>> Posted via http://www.ruby-forum.com/.
> 
> A 2-dimensional array is simply an array of arrays. Something like this:
> 
> a = Array.new() {Array.new}
> 
> Or you could use the Matrix class from "matrix" in the standard library.

A 2 dimensional array as an array of arrays is a lowest common 
denominator.  It assumes that I want only to use it as a simple storage 
mechanism.  What I want is a 2 dimensional array data structure that has 
powerful operating mechanisms such as sorting.  Additionally the way an 
array of arrays is treated in Ruby goes against what is intuitive or 
expected; and it was my understanding that Ruby was supposed to be 
designed to do what "least surprises".

Here is a simple example.

a = Array.new(){Array.new()}
b = [9,8,7]
c = [1,2,3]
a[0] = b
a[1] = c

puts a.sort
=>[[1,2,3],[9,8,7]]

So this allows a sort across the entire array and it should be noted 
that it does an index step through comparison so [1,1,2] would come 
after [1,1,1].  However this means I am limited to sorting only via this 
mechanism.

Based on Ruby syntax I would find this to be intuitive.

a[0..1][0].sort

The results I would then expect would be
[[1],[9]]

The results I actually get from this are
[7,8,9]

What is happening is that in a[0..1][0] a[0..1] is grabbing the subset 
of arrays 0 to 1 and then the second index [0] is indexing back in to 
the subset.  What looks like it should be happening is that a[0..1][0] 
is defining the set of the arrays where we wish to retrieve the 0 index.

-- 
Posted via http://www.ruby-forum.com/.