From: redstun <redstun@...>
Date: 2011-01-28T00:10:41+09:00
Subject: Re: Enumerable.inject_with_index?

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guess we find a spot to improve when chaining up multiple enum methods?

btw, looks like you guys both have more powerful computer than mine. ;-)


On Thu, Jan 27, 2011 at 9:10 PM, Benoit Daloze <eregontp@gmail.com> wrote:

> On 27 January 2011 01:42, redstun <redstun@gmail.com> wrote:
> > Interesting, thanks Colin.
> >
> > As you said, the code you demonstrated, could performer better, meanwhile
> > it's somewhat less elegant.
> >
> > IMHO the code is ok, we just have more space inside the
> > interpreter/runtime to get improved, like in JVM, the JIT compiler could
> > compile all of the 4 lines of code in to the same machine instructions
> and
> > yield the same performance.
> >
> > The dynamic nature and elegance design of Ruby certainly sacrificed
> > performance at somewhat level, but  that doesn't stop you and me from
> using
> > it, right? :-)
> >
> > Anyway, thanks for the benchmark demo, I just ran it on my machine, with
> > both MRI and JRuby,
> > MRI 1.8.7
> >                                user     system      total        real
> > each_with_index.inject(0)   4.930000   0.000000   4.930000 (  5.036288)
> > inject(0)                   3.088000   0.000000   3.088000 (  3.080176)
> > each_with_index             2.668000   0.000000   2.668000 (  2.668153)
> > each                        1.700000   0.000000   1.700000 (  1.713098)
> >
> > JRuby 1.5.6
> >                                user     system      total        real
> > each_with_index.inject(0)   1.918000   0.000000   1.918000 (  1.918000)
> > inject(0)                   1.058000   0.000000   1.058000 (  1.058000)
> > each_with_index             0.979000   0.000000   0.979000 (  0.979000)
> > each                        0.624000   0.000000   0.624000 (  0.624000)
> >
> > Like your result the raw each runs the fastest, but we can also find
> that,
> > the result of each_with_index.inject with JRuby is already close to that
> of
> > raw each with MRI.
> >
> >
> > On Tue, Jan 25, 2011 at 5:43 AM, Colin Bartlett <colinb2r@googlemail.com
> >wrote:
> >
> >> I'm curious as to when and why people use each_with_index and/or
> >> inject, etc, instead of a somewhat less elegant, and admittedly
> >> possibly less flexible, more direct approach. (Which usually(?) takes
> >> about the same number of characters for the code.)
> >>
> >> ary = [3, 4, 5]
> >> rrr = ary.each_with_index.inject(0) { |sum, (v, index)| sum + v * index
> }
> >> p rrr #=> 14
> >> index = -1; rrr = ary.inject(0) { |sum, v| index += 1; sum + v * index }
> >> p rrr #=> 14
> >> rrr = 0; ary.each_with_index { |v, index| rrr += v * index }; rrr
> >> p rrr #=> 14
> >> index = -1; rrr = 0; ary.each { |v| index += 1; rrr += v * index }; rrr
> >> p rrr #=> 14
> >>
> >> require "benchmark"
> >> kt = 500_000
> >> Benchmark.bmbm() do |bm|
> >>  bm.report( "each_with_index.inject(0)" ) { kt.times {
> >>   rrr = ary.each_with_index.inject(0) { |sum, (v, index)| sum + v *
> index }
> >>  } }
> >>  bm.report( "inject(0)"                 ) { kt.times {
> >>   index = -1; rrr = ary.inject(0) { |sum, v| index += 1; sum + v * index
> }
> >>  } }
> >>  bm.report( "each_with_index"           ) { kt.times {
> >>   rrr = 0; ary.each_with_index { |v, index| rrr += v * index }
> >>  } }
> >>  bm.report( "each"                      ) { kt.times {
> >>   index = -1; rrr = 0; ary.each { |v| index += 1; rrr += v * index }
> >>  } }
> >> end
> >>
> >> #=>
> >> Rehearsal -------------------------------------------------------------
> >> each_with_index.inject(0)   2.410000   0.000000   2.410000 (  2.404242)
> >> inject(0)                   1.000000   0.000000   1.000000 (  1.000677)
> >> each_with_index             0.840000   0.010000   0.850000 (  0.846287)
> >> each                        0.640000   0.000000   0.640000 (  0.640142)
> >> ---------------------------------------------------- total: 4.900000sec
> >>
> >>                                user     system      total        real
> >> each_with_index.inject(0)   2.380000   0.020000   2.400000 (  2.392590)
> >> inject(0)                   1.000000   0.000000   1.000000 (  0.999785)
> >> each_with_index             0.850000   0.000000   0.850000 (  0.846178)
> >> each                        0.640000   0.000000   0.640000 (  0.639366)
> >>
> >> (My apologies if the benchmarks are ragged and unaligned.)
> >>
> >>
> >
>
> Just to complete with 1.9 (ruby 1.9.3dev (2011-01-26 trunk 30659)
> [x86_64-darwin10.6.0]) results:
>
> Rehearsal -------------------------------------------------------------
> each_with_index.inject(0)   1.220000   0.000000   1.220000 (  1.220411)
> inject(0)                   0.560000   0.000000   0.560000 (  0.568007)
> each_with_index             0.510000   0.010000   0.520000 (  0.516797)
> each                        0.400000   0.000000   0.400000 (  0.405471)
> ---------------------------------------------------- total: 2.700000sec
>
>                                user     system      total        real
> each_with_index.inject(0)   1.250000   0.000000   1.250000 (  1.268727)
> inject(0)                   0.570000   0.010000   0.580000 (  0.582921)
> each_with_index             0.510000   0.000000   0.510000 (  0.510591)
> each                        0.390000   0.000000   0.390000 (  0.401833)
>
> Only each_with_index.inject is notably slower, others are similar.
>
>

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