From: Robert Klemme <shortcutter@...>
Date: 2012-01-23T23:31:38+09:00
Subject: Re: uniq with count; better way?

On Mon, Jan 23, 2012 at 3:08 PM, Karsten Meier
<developer@handylearn-projects.de> wrote:
> Ok, I tried some benchmarks. We have now even more variables, as they
> also depend on "maxval" from the dataset.
>
> maxval = 1000
> ar = [].tap{|a| 1_000_000.times {a << rand(maxval)}}
>
> b.report("Meier:") {
>  n.times {
>    hist =  Array.new(maxval+1, 0)
>    ar.each{|x| hist[x] += 1;}
>    result = Hash.new(0)
>    0.upto(maxval){|i| result[i] = hist[i] unless hist[i] == 0}

You could also do

result.each_with_index {|c,i| result[i] = c if c.nonzero?}

>    result
>  }
> }

That's just part of the testing code, isn't it?  Why not share the
complete code?

> On my jruby and my windows- mri 1.8.7 my algorithm was fastest for
> maxvalue of 10, 100 or 10000, for example:
>
> SIZE
> 1000000
> MAXVAL
> 10000
>                     user     system      total        real
> Ralph Shneiver:  0.533000   0.000000   0.533000 (  0.518000)
> Meier:           0.312000   0.000000   0.312000 (  0.312000)
> Keinich #1       0.814000   0.000000   0.814000 (  0.814000)
>
> (I have no 1.9.3 yet on my windows PC, so it may be different there)
>
> But here are two observations:
> 1) speed-up is not so big as I expected. In C, I expect array lookup to
> be factors better than hash calculation (followed by an array-lookup in
> the hash-table...). In Ruby it seem to be not so much faster. But the
> speedup gets bigger for bigger values of maxval.
>
> 2) My algorithm sometimes run much much slower when #kennich1 had run
> before mine. :-( It seem to get worse with big values of maxval, but not
> with jruby --1.9 option. It is not the array-allocate itself that is the
> problem.
> Is it possible that group_by changes the internal array structure, So I
> get a non-continous-array?

No.  It's more likely that you are hit by GC I'd say.  You could also
try Benchmark.bmbm for warm up before the test.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/