From: Brad Phelan <phelan@...>
Date: 2007-05-31T03:25:26+09:00
Subject: Re: Enumerable#serially - those nifty functions w/o memory footprint

Brad Phelan wrote:
> Brad Phelan wrote:
>> Brian Candler wrote:
>>> On Wed, May 30, 2007 at 10:46:33PM +0900, SonOfLilit wrote:
>>>> Sorry, found a bug, I'll need to make it into this:
>>>>
>>>> module Enumerable
>>>>  def serially(&b)
>>>>    a = []
>>>>    self.each{|x| t = ([x].instance_eval(&b); a << b[0] unless b.empty?}
>>>>    # notice, relevance to "it" discussion that's currently going on, 
>>>> just    btw
>>>>  end
>>>> end
>>>
>>> Somehow I don't think you tested this :-)
>>>
>>> * You have mismatched parentheses
>>> * You assign to t, but never use the value
>>> * you call b twice, once with no arguments, and once with 0 as an 
>>> argument
>>> * b is a block, but you call #empty? on it
>>>
>>> Can you give an example of how this is supposed to be used?
>>>
>>> Brian.
>>>
>>
>> I think I get his point. I wrote a little lib to try out my 
>> interpretation of what he is trying to do.
>>
>>
>> a = (1..20)
>>
>> b = a.serially do
>>     select do |x|
>>         if x > 10
>>             true
>>         else
>>             false
>>         end
>>     end
>>     collect do |x|
>>         "0x" + x.to_s
>>     end
>>     select do |x|
>>         if x == "0x15"
>>             false
>>         else
>>             true
>>         end
>>     end
>> end
>>
>> puts b
>>
>>
>>
>> # generates
>>
>> 0x11
>> 0x12
>> 0x13
>> 0x14
>> 0x16
>> 0x17
>> 0x18
>> 0x19
>> 0x20
>>
>> The lib is at
>>
>> http://xtargets.com/snippets/posts/show/69
>>
>> -- 
>> Brad Phelan
>> http://xtargets.com/snippets
>>
> 
> A quick profile with ruby-prof find the above technique about 10 times 
> slower in 50000 elements than for the traditional method.
> 
> -- 
> Brad Phelan
> http://xtargets.com

This little bit of code has got me interested. Turns out I can create a 
version with comparable time execution by slicing the the input 
enumerable into memory friendly chunks and then performing all
operations on those chunks. This kind of reminds me of C++
expression templating tricks

See the link

http://xtargets.com/snippets/posts/show/69

for the latest highspeed version and the ruby-prof results

--
Brad Phelan
http://xtargets.com