gistfile1.txt

$ cat bench-hash-creation.rb
require 'benchmark'

n = 1_000_000

Benchmark.bm do |x|
  x.report('arrays') {
    k = []
    v = []

    for i in 1..n do
      k << i
      v << i  
    end

    Hash[*k.zip(v).flatten]
  }

  x.report('direct') {
    h = {}
    
    for i in 1..n do
      h[i] = i
    end
  }
end

$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]
$ ruby bench-hash-creation.rb 
      user     system      total        real
arrays  2.740000   0.350000   3.090000 (  3.389127)
direct  1.040000   0.290000   1.330000 (  1.430653)

$ jruby -v
jruby 1.3.1 (ruby 1.8.6p287) (2009-06-15 2fd6c3d) (Java HotSpot(TM) Client VM 1.6.0_14) [i386-java]
$ jruby --server bench-hash-creation.rb 
      user     system      total        real
arrays861.593000   0.000000 861.593000 (861.506000)
direct  4.180000   0.000000   4.180000 (  4.180000)