From: Ryan Davis <ryand-ruby@...>
Date: 2012-01-09T12:38:36+09:00
Subject: Re: NArray - from coordinates to index


On Jan 8, 2012, at 13:15 , Satsou Sa wrote:

> Hi,
> 
> How can we convert a coordinates to an index?
> 
> I'm using the awesome NArray library with some arrays of 1, 2, 3, or
> more dimensions.  For instance, if we consider this 3x3 array of 2
> dimensions ...
> 
>    NArray.int(3,3):
>    [ [ 0, 0, 0 ],
>      [ 0, 0, 0 ],
>      [ 0, 0, 0 ] ]
> 
> ... the square of the coordinate [0,1] have also the index of 3 (and
> according to the NArray specs, a[3] is same as a[0,1] if a is 3x3
> array).
> 
> Is there a simple way to find the index, from the coordinates?

Use the coordinates as a base N number to convert to a base 10 index:

a[0,1] == 10b3 == 1*3^1+0*3^0 == 1*3+0*1 == 3