From: Phrogz <phrogz@...>
Date: 2009-06-17T09:50:07+09:00
Subject: Re: Extracting and inserting a "column" from/into an array

On Jun 16, 9:34 am, Chauk-Mean Proum <chauk.m...@gmail.com> wrote:
> Hi,
>
> For image processing, I have to do the following operations :
>
> 1/ I have an array and I want to extract every 4 element into another
> array :
>
> # r=red, g=green, b=blue, a=alpha
> img_data = [ "r1", "g1", "b1", "a1", "r2, "g2", "b2", "a2" ]
>
> => [ "a1", "a2" ]  # the array of every four elements i.e. alpha data
>
> It's like extracting the fourth column of a matrix of n rows and 4
> columns.
>
> 2/ Conversely, I have an array and I need to add elements at every 3
> elements
>
> img_data = [ "r1", "g1", "b1", "r2, "g2", "b2" ]
> alpha_data = [ "a1", "a2" ] # the elements to add
>
> => [ "r1", "g1", "b1", "a1", "r2, "g2", "b2", "a2" ]
>
> It's like inserting a column to a matrix of n rows and 3 columns.
>
> I'm wondering if there is an easy or seamless way to do these
> operations.

Possibly not as efficient, but if you were representing the data as a
'2D' array (array of arrays) alternatively you could .transpose the
array, insert a row, and .transpose it back.