From: Ammar Ali <ammarabuali@...>
Date: 2010-10-30T07:36:13+09:00
Subject: Re: Is this an effective loop

--0016368e2294d84f590493c9151c
Content-Type: text/plain; charset=UTF-8

On Sat, Oct 30, 2010 at 12:24 AM, Jeremy Bopp <jeremy@bopp.net> wrote:

> On 10/29/2010 4:59 PM, Ammar Ali wrote:
> > Indeed, a benchmark is the best way to find out. Here's a quick one, with
> > slight changes to your original code and no puts, and including Jeremy's
> > idiomatic suggestion.
>
> <snip>
>
> > The numbers I got on my machine are:
> >
> > for loop  1.210000   0.000000   1.210000 (  1.225631)
> > while loop  1.460000   0.010000   1.470000 (  1.469653)
> > times loop  1.980000   0.000000   1.980000 (  1.998238)
> >
> > I expected the times version to be faster too, but it looks like the for
> > loop is the fastest in this case.
>
> This is interesting, and in an effort to get slightly more accurate data
> on this microbenchmark, I tweaked your code a bit to ensure that the
> loops are performing the same work in each case.  I then looped the test
> 5 times:
>
> require 'benchmark'
>
> count = 1_000_000
> 5.times do
>   Benchmark.benchmark do |bm|
>    bm.report("for loop") {
>       for i in 0..count-1
>        i += 1
>         i * i
>      end
>    }
>
>    bm.report("while loop") {
>       i = 0
>      while i < count
>        i += 1
>        i * i
>      end
>    }
>
>    bm.report("times loop") {
>      count.times do |i|
>        i += 1
>        i * i
>      end
>    }
>  end
>
>  puts
> end
>
> =>
> for loop  1.656000   0.000000   1.656000 (  1.888000)
> while loop  1.750000   0.000000   1.750000 (  1.860000)
> times loop  1.735000   0.000000   1.735000 (  1.954000)
>
> for loop  1.984000   0.000000   1.984000 (  1.980000)
> while loop  1.625000   0.000000   1.625000 (  1.848000)
> times loop  1.813000   0.000000   1.813000 (  1.967000)
>
> for loop  1.797000   0.000000   1.797000 (  1.923000)
> while loop  1.687000   0.000000   1.687000 (  1.850000)
> times loop  1.938000   0.000000   1.938000 (  1.956000)
>
> for loop  1.687000   0.000000   1.687000 (  1.902000)
> while loop  1.813000   0.016000   1.829000 (  1.842000)
> times loop  1.718000   0.000000   1.718000 (  1.943000)
>
> for loop  1.782000   0.000000   1.782000 (  1.901000)
> while loop  1.734000   0.000000   1.734000 (  1.843000)
> times loop  1.734000   0.000000   1.734000 (  1.956000)
>
>
> As can be seen, there is a fair bit of variance in the benchmark.  There
> does not appear to be a clear winner overall.
>
> -Jeremy
>
>

I see. I excluded the i += 1 from the for and times loops because that is
done automatically. Adding them seemed to add work that was not necessary
for those constructs, and IMHO, make the benchmark inaccurate.

Regards,
Ammar

--0016368e2294d84f590493c9151c--