From: Robert Klemme <shortcutter@...>
Date: 2007-05-31T17:45:28+09:00
Subject: Re: Enumerable#serially - those nifty functions w/o memory footprint

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On 30.05.2007 21:54, SonOfLilit wrote:
> Following is ruby-prof output. First, a few words:
> 
> 4.75 against 1.56 isn't too good, but it isn't ten times slower. I
> think it can be excused (and maybe the code can be optimized a bit) in
> cases where you'd process huge lists with ruby of all languages.
> 
> This is the code used to profile:
> 
> require 'rubygems'
> require 'ruby-prof'
> 
> module Enumerable
> def serially(&b)
>   a = []
>   self.each{|x| t = [x].instance_eval(&b); a << t[0] unless t.empty?}
>   a
> end
> end
> 
> # Profile the code
> result = RubyProf.profile{
> a = (1..50000)
> b = a.serially{select{|x| x>280}.collect{|x|"0x" <<
> x.to_s}.select{|x| x != "0x15"}}
> }
> 
> # Print a graph profile to text
> printer = RubyProf::GraphPrinter.new(result)
> printer.print(STDOUT, 0)
> 
> result = RubyProf.profile{
> a = (1..50000)
> b = a.select{|x| x>280}.collect{|x|"0x" << x.to_s}.select{|x| x != "0x15"}
> }
> 
> # Print a graph profile to text
> printer = RubyProf::GraphPrinter.new(result)
> printer.print(STDOUT, 0)

You are changing subject in between:  Originally you started out with 
memory consumption being the issue.  Now you talk about speed.  Your 
solution is neither fast nor easy on the memory.  For speed see the 
benchmark below.  It's not easy on the memory because you still create a 
*ton* of temporary one element arrays (four per iteration if I'm not 
mistaken) - this avoids the single large copy but allocating and GC'ing 
all these temporaries imposes a significant overhead.  The obvious and 
simple solution here is to do it all in *one* iteration.  So why invent 
something new if there is an easy and efficient solution available?

Kind regards

	robert


10:38:35 [Temp]: ./ser.rb
Rehearsal --------------------------------------------------
classic          3.359000   0.000000   3.359000 (  3.338000)
serially        13.719000   0.016000  13.735000 ( 13.747000)
serially!       13.328000   0.000000  13.328000 ( 13.361000)
inject           4.297000   0.000000   4.297000 (  4.339000)
each             3.297000   0.000000   3.297000 (  3.273000)
---------------------------------------- total: 38.016000sec

                      user     system      total        real
classic          3.203000   0.000000   3.203000 (  3.265000)
serially        12.891000   0.000000  12.891000 ( 13.233000)
serially!       12.438000   0.000000  12.438000 ( 12.617000)
inject           3.937000   0.000000   3.937000 (  3.985000)
each             2.937000   0.000000   2.937000 (  3.008000)



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#!ruby

require 'benchmark'

ITER = 10

module Enumerable
  def serially(&b)
    a = []
    each{|x| t = [x].instance_eval(&b); a << t[0] unless t.empty?}
    a
  end
end

a = (1..50000)

Benchmark.bmbm(15) do |bench|
  bench.report("classic") do
    ITER.times do
      # a = (1..50000)
      b = a.select {|x| x>280}.collect{|x|"0x" << x.to_s}.select{|x| x != "0x15"}
   end
  end

  bench.report("serially") do
    ITER.times do
      # a = (1..50000)
      b = a.serially { select {|x| x>280}.collect{|x|"0x" << x.to_s}.select{|x| x != "0x15"} }
   end
  end

  bench.report("serially!") do
    ITER.times do
      # a = (1..50000)
      b = a.serially { select {|x| x>280}.collect! {|x|"0x" << x.to_s}.select {|x| x != "0x15"} }
   end
  end

  bench.report("inject") do
    ITER.times do
      # a = (1..50000)
      b = a.inject([]) do |acc, x|
        if x > 280
          x = "0x" << x.to_s
          acc << x unless x == "0x15"
        end
        acc
      end
    end
  end

  bench.report("each") do
    ITER.times do
      # a = (1..50000)
      b = []
      a.each do |x|
        if x > 280
          x = "0x" << x.to_s
          b << x unless x == "0x15"
        end
      end
    end
  end
end

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