From: Robert Klemme <shortcutter@...>
Date: 2005-08-29T18:42:02+09:00
Subject: Re: how to unflatten a flat-array

2005/8/29, SHIGETOMI, Takuhiko <tshiget1@gw.nsw.co.jp>:
> greetings, William. i'm sorry, your way is beyond my light-weight brain.

Although I'm not the author I can jump in with an explanation.

> > ary = [1,2,3,4,5,6,7,8]
> > f=nil
> > t=ary.partition{f=!f}
> > p t[0].zip(t[1])
> 
> but it works...

#partition puts contents of an Enumerable into two arrays depending on
the boolean result of a block. For example:

>> (0...10).partition {|x| x % 2 == 0}
=> [[0, 2, 4, 6, 8], [1, 3, 5, 7, 9]]

The code above just toggles a flag (f) on each evaluation of the block
thus putting elements into the first and second array returned
interchangingly.

Array#zip basically iterates two array in lock step.  So the first
partition contains x elements and the second partition contains y
elements and #zip creates pairs [x,y] from them.

Although I like this solution because of its cuteness and shortness,
it has the disadvantage of creating two intermediate arrays.  That
might or might not be a problem in your case - depending on the array
sizes involved. HTH

Kind regards

robert