From: Larry Evans <cppljevans@...>
Date: 2011-01-08T13:00:23+09:00
Subject: Re: Nooby question : multidimensional arrays.

On 01/07/11 17:56, Kedar Mhaswade wrote:
> Is this an okay job of implementing a multidimensional array?
> 
> https://github.com/kedarmhaswade/datacube/blob/master/data_cube.rb
> 
> Thank you for any feedback.
> 
> -Kedar
> 
There's a book:

  http://web.engr.oregonstate.edu/~budd/Books/aplc/

which describes an expansion vector which is a scan of
the array sizes.  IOW, for:

  arr = Array.new(s0,s1,...sn)

the expansion vector for this arr is:

  arr.ev = [1, s0, s0*s1, s0*s1*s3,..., s0*s1*...*sn]


The i-th element of arr.ev is the distance between successive
elements in the i-th dimension.  IOW:

  the locatoin of:
    arr[i0,i1,..., ij, ... in]
  is located arr.ev[j] elements from:
    arr[i0,i1,..., ij+1, ... in]

IOW:

    arr[i0,i1,..., ij, ... in]

is located:

    i0*arr.ev[0]+i1*arr.ev[1]+...+in*arr.ev[n]

elements from the 1st element:

    arr[0,0,...,0]

Thus, given the sizes, you can create a member variable
which is the expansion vector, then use that to access the
elements by calculating the offset from the initial element
using the dot product:

    i0*arr.ev[0]+i1*arr.ev[1]+...+in*arr.ev[n]

HTH.

Good luck.