From: Joel VanderWerf <vjoel@...>
Date: 2002-09-20T10:46:32+09:00
Subject: Re: How to Efficiently Calculate the Pattern of Zeros and Ones?


No doubt the state machine approach is faster, and you're also accurate 
about shifting. I'm just relieved that each_with_neighbors doesn't spew 
garbage, which would make it even slower :-)

William Djaja Tjokroaminata wrote:
> Hi,
> 
> If the "shifts data through it" is accomplished using Ruby
> Array#push() and Array#shift(), then probably the code is indeed very easy
> to write, but probably not very efficient in the background.  I like the
> answer given in the first response, as I think it mimics how regular
> expression works (using some "states").
> 
> Regards,
> 
> Bill
> ===========================================================================
> Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
> 
>>I had to go back and check whether each_with_neighbors generated lots of 
>>arrays or not. It turns out that it doesn't. Instead, it keeps a single 
>>array, shifts data through it, and yields the array. So it should be 
>>fairly efficient as pure ruby code goes.
> 
> 
>>However, this may surprise users who modify the array in the iterator 
>>block, so I'll slip a warning into the docs.
> 
> 
>>If your rows are short, each_with_neighbors is not very efficient 
>>because of the "warm up" and "cool down" to deal with the cases near the 
>>edge.
> 



-- 
Joel VanderWerf                          California PATH, UC Berkeley
mailto:vjoel@path.berkeley.edu                     Ph. (510) 231-9446
http://www.path.berkeley.edu                       FAX (510) 231-9512