From: Trans <transfire@...>
Date: 2006-12-27T08:34:39+09:00
Subject: Re: Hash with two identical keys?


William James wrote:
> Here's a speed comparison for various numbers of keys:
>
> require 'benchmark'
>
> $iterations = 40_000
>
> def rand_sym
>   letters = ('a'..'z').to_a
>   sym = ""
>   8.times{ sym << letters[ rand(letters.size) ] }
>   sym.to_sym
> end
>
> def test_assoc n
>   alist = []
>   keys = []
>   while alist.size < n do
>     key = rand_sym
>     unless keys.include?( key )
>       alist << [ key, true ]
>       keys << key
>     end
>   end
>   $iterations.times{
>     keys.each{|key|  fail if alist.assoc(key)[1] != true }
>   }
> end
>
> def test_hash n
>   hash = {}
>   keys = []
>   while hash.size < n
>     key = rand_sym
>     unless hash.include?( key )
>       hash[key] = true
>       keys << key
>     end
>   end
>   $iterations.times{
>     keys.each{|key|  fail if hash[key] != true }
>   }
> end
>
> Benchmark.bm(8) do |x|
>   [1,2,3,7,20].each{ |n|
>     x.report("assoc %2d" % n) { test_assoc n }
>     x.report("hash  %2d" % n)  { test_hash n  }
>   }
> end
>
>               user     system      total        real
> assoc  1  0.150000   0.000000   0.150000 (  0.171000)
> hash   1  0.130000   0.000000   0.130000 (  0.140000)
> assoc  2  0.291000   0.000000   0.291000 (  0.310000)
> hash   2  0.200000   0.000000   0.200000 (  0.231000)
> assoc  3  0.440000   0.000000   0.440000 (  0.460000)
> hash   3  0.291000   0.000000   0.291000 (  0.311000)
> assoc  7  1.172000   0.000000   1.172000 (  1.252000)
> hash   7  0.590000   0.000000   0.590000 (  0.640000)
> assoc 20  5.188000   0.000000   5.188000 (  5.578000)
> hash  20  1.652000   0.000000   1.652000 (  1.813000)

Nice. Doesn't matter a whole lot a few keys but there is a clear slow
down.

I came up with another possibility however. I won;t work for all cases,
but using Marshal.dup on the args instead of converting to assoc gives
the proper result too. Wonder how that would benchmark?

T.