From: Hashmal <jeremypinat@...>
Date: 2011-05-09T08:25:29+09:00
Subject: Re: Index to coordinates conversion, according the matrix shape

This is a perfect case for modulo (%). It gives the remainder of a division.

     def index_to_coordinates arr_size, index
       x = index % arr_size[0]
       y = (index - x) / arr_size[0]
       return x, y
     end

     coordinates [3, 3], 3 # => [0, 1]

You will notice that the "matrix height" (arr_size[1]) is not used for 
the calculation. However, you might want to check that the index you ask 
is not out of bounds.

PS: I usually make some stupid mistakes when doing math, so the code 
above may be incorrect. However, the basic idea is here: modulo.



On 5/9/11 12:14 AM, Paul A. wrote:
> Hello,
>
> I would like to converte an index (of a flatten array) to a
> multi-dimensions coordinates (of the multi-dimensions version of the
> previous flatten array).
>
> Example:
>
> Considering the following 2 dimensions array (3x3):
>
>      [ [ -, -, - ],
>        [ *, -, - ],
>        [ -, -, - ] ]
>
> We can see that, the coordinates of the checked case is [0, 1].
>
> Now, if we flat this array, it looks like:
>
>      [ -, -, -, *, -, -, -, -, - ]
>
> Here, we can see the coordinate (or the index) of the checked case is 3.
>
> But how can we do the opposite? I mean, a method looking like:
>
>      index_to_coordinates([3, 3], 3) # =>  [0, 1]
>
> Thanks!
>