From: Robert Klemme <shortcutter@...>
Date: 2008-03-08T00:02:07+09:00
Subject: Re: duplicating characters in a string

2008/3/6, Joel VanderWerf <vjoel@path.berkeley.edu>:
> Rodrigo Bermejo wrote:
>  > "abc".gsub(/./) { |x| x * 2 }
>
>
> That's the most elegant way to refer to captures, but if speed matters:
>
>  "abc".gsub(/(.)/, "\\1\\1")
>
>  The "\\1" is always easy to mess up, which is why I generally prefer the
>  block form.
>
>  It's only about a factor of two faster, according to the following, but
>  that matters sometimes.


>  Rehearsal ---------------------------------------------------
>  s.gsub(re){...}   5.970000   0.000000   5.970000 (  6.009089)
>  s.gsub(re,...)    2.900000   0.060000   2.960000 (  3.148006)
>  ------------------------------------------ total: 8.930000sec
>
>                        user     system      total        real
>  s.gsub(re){...}   5.760000   0.010000   5.770000 (  5.925049)
>  s.gsub(re,...)    2.800000   0.060000   2.860000 (  2.914432)

What version did you test with? I get much more dramatic differences:

15:56:11 ~
$ ruby /c/Temp/gs.rb
Rehearsal -----------------------------------------------------------
s.gsub(re){|x| x * 2}    25.313000   0.031000  25.344000 ( 25.354000)
s.gsub(re){|x| x << x}   22.812000   0.000000  22.812000 ( 22.845000)
s.gsub(re, '\1\1')        6.516000   0.015000   6.531000 (  6.539000)
s.gsub(re, '\&\&')        6.578000   0.016000   6.594000 (  6.595000)
s.gsub(/./){|x| x * 2}   25.172000   0.016000  25.188000 ( 25.182000)
s.gsub(/./){|x| x << x}  22.843000   0.000000  22.843000 ( 22.857000)
s.gsub(/(.)/, '\1\1')     6.344000   0.015000   6.359000 (  6.355000)
s.gsub(/./, '\&\&')       6.188000   0.032000   6.220000 (  6.217000)
------------------------------------------------ total: 121.891000sec

                              user     system      total        real
s.gsub(re){|x| x * 2}    25.484000   0.015000  25.499000 ( 25.502000)
s.gsub(re){|x| x << x}   22.813000   0.031000  22.844000 ( 22.856000)
s.gsub(re, '\1\1')        6.312000   0.000000   6.312000 (  6.337000)
s.gsub(re, '\&\&')        6.359000   0.000000   6.359000 (  6.359000)
s.gsub(/./){|x| x * 2}   25.922000   0.000000  25.922000 ( 25.994000)
s.gsub(/./){|x| x << x}  22.672000   0.015000  22.687000 ( 22.707000)
s.gsub(/(.)/, '\1\1')     6.375000   0.016000   6.391000 (  6.389000)
s.gsub(/./, '\&\&')       6.235000   0.000000   6.235000 (  6.239000)
16:00:22 ~
$ ruby -v
ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-cygwin]
16:00:26 ~
$ cat /c/Temp/gs.rb
require 'benchmark'

s = ("abc" * 1_000_000).freeze
re = /(.)/
re2 = /./

Benchmark.bmbm do |b|
  b.report("s.gsub(re){|x| x * 2}") do
    s.gsub(re) { |x| x * 2 }
  end

  b.report("s.gsub(re){|x| x << x}") do
    s.gsub(re) { |x| x << x }
  end

  b.report("s.gsub(re, '\\1\\1')") do
    s.gsub(re, "\\1\\1")
  end

  b.report("s.gsub(re, '\\&\\&')") do
    s.gsub(re, "\\&\\&")
  end


  b.report("s.gsub(/./){|x| x * 2}") do
    s.gsub(/./) { |x| x * 2 }
  end

  b.report("s.gsub(/./){|x| x << x}") do
    s.gsub(/./) { |x| x << x }
  end

  b.report("s.gsub(/(.)/, '\\1\\1')") do
    s.gsub(/(.)/, "\\1\\1")
  end

  b.report("s.gsub(/./, '\\&\\&')") do
    s.gsub(/./, "\\&\\&")
  end
end
16:00:31 ~
$

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end