From: Kristof Bastiaensen <kristof@...>
Date: 2004-09-04T07:50:26+09:00
Subject: Re: autochomp?

Hi,

On Fri, 03 Sep 2004 18:03:35 +0200, Robert Klemme wrote:

> 
> "Kristof Bastiaensen" <kristof@vleeuwen.org> schrieb im Newsbeitrag
> news:pan.2004.09.02.20.13.44.101750@vleeuwen.org...
>> Hi,
>>
>> On Thu, 02 Sep 2004 19:18:10 +0200, Robert Klemme wrote:
>>
>>
>> > "Martin DeMello" <martindemello@yahoo.com> schrieb im Newsbeitrag
>> > news:idIZc.301315$J06.4478@pd7tw2no...
>> >> [quoted text muted]
>> >
>> > Not AFAIK.  You can do
>> >
>> > content = IO.readlines(file).each {|l| l.chomp!}
>> >
>> > or (more efficient)
>> >
>> > content = File.open(file) {|io| io.inject([]) {|ar,line| line.chomp!;
>> > ar << line} }
>> >
>> >
>> I think in this case the first is more efficient than the second. Since
>> chomp! modifies the object inplace, no object gets created.
> 
> ???  Please read again.  The first is less efficient because it iterates
> through the lines of the file twice and both use inplace modification
> (#chomp!).
> 
> Kind regards
> 
>     robert

It would seem logical, but benchmarking shows different:

#---- begin filetest.rb ---- 
require 'benchmark'

file = "testfile.txt"
Benchmark.bm(7) do |x|
   x.report("readlines:") do
      IO.readlines(file).each {|l| l.chomp!}
   end

   x.report("inject:") do
      File.open(file) {|io| io.inject([]) {
            |ar,line| line.chomp!; ar << line}}
   end

   x.report("foreach:") do
      IO.foreach(file){|line| (lines||=[]) << line.chomp!}
   end
end
#---- end filetest.rb -----

$ seq 10000 > testfile.txt
$ ruby filetest.rb
readlines:  0.050000   0.010000   0.060000 (  0.085483)
inject:  0.130000   0.010000   0.140000 (  0.172144)
foreach:  0.080000   0.000000   0.080000 (  0.112690)

Regards,
KB