From: Tim Greer <tim@...>
Date: 2009-01-11T09:19:34+09:00
Subject: Re: Q: most efficient way to remove duplicate spaces in a string?

pat eyler wrote:

> On Sat, Jan 10, 2009 at 1:14 PM, Tim Greer <tim@burlyhost.com> wrote:
>> For gsub/gsub!, instead of replacing one or more white space with a
>> white space, speed it up by replacing two or more white space with a
>> white space.  This saves unneeded processing by not replacing single
>> white space.  I.e., instead of gsub(/ +/, ' '), try gsub(/  +/, ' ')
>> or
>> gsub(/ {2,}/, ' ') and benchmark them (they should be faster).  Of
>> course, it's still not going to be as fast as split.join or
>> squeeze.strip (at least depending on the version of ruby used, as
>> older ruby versions may put squeeze.strip markedly slower than
>> split.join.
> 
> #!/usr/bin/ruby
> 
> require 'benchmark'
> 
> n = 1_000_000
> 
> Benchmark.bm(15) do |x|
>   x.report("gsub") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.gsub(/ +/, ' ')
>     end
>   }
>   x.report("gsub!") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.gsub!(/ +/, ' ')
>     end
>   }
>   x.report("gsub2") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.gsub(/ {2,}/, ' ')
>     end
>   }
>   x.report("gsub!2") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.gsub!(/ {2,}/, ' ')
>     end
>   }
>   x.report("gsub s") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.gsub(/\s+/, ' ')
>     end
>   }
>   x.report("gsub! s") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.gsub!(/\s+/, ' ')
>     end
>   }
>   x.report("gsub2 s") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.gsub(/\s{2,}/, ' ')
>     end
>   }
>   x.report("gsub!2 s") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.gsub!(/\s{2,}/, ' ')
>     end
>   }
>   x.report("split.join") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.split.join(' ')
>     end
>   }
>   x.report("squeeze.strip") { n.times do
>       a_string = "This     is  a test   string."
>       a_string.squeeze(' ').strip
>     end
>   }
> end
> 
> 
> $ ./stringcleanup.rb
>                      user     system      total        real
> gsub             7.250000   0.120000   7.370000 (  8.386002)
> gsub!            7.240000   0.130000   7.370000 (  9.007479)
> gsub2            7.110000   0.140000   7.250000 (  9.302915)
> gsub!2           6.830000   0.150000   6.980000 (  9.309362)
> gsub s           7.410000   0.140000   7.550000 ( 10.864572)
> gsub! s          7.400000   0.130000   7.530000 ( 10.286886)
> gsub2 s          7.020000   0.100000   7.120000 (  8.977424)
> gsub!2 s         6.860000   0.100000   6.960000 (  8.421220)
> split.join       4.420000   0.110000   4.530000 (  5.716684)
> squeeze.strip    3.120000   0.110000   3.230000 (  3.651918)
> 
> 
> I haven't run it enough to do any statistical analysis, but after
> 5 runs it seems like the various flavors of gsub/gsub! don't really
> perform any differently.  splitting and squeezing look like much
> better options.
> 
> 
> 

Yeah, it doesn't make a huge difference, but it's just a little faster
is all.  Definitely split.join is faster.  squeeze.strip is the fastest
(though that will actually take longer on older versions of ruby).  My
follow up was really just a reference for gsub/gsub!, not that it would
be faster than the other two. :-)
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