From: chr_news@... (chr_news@...)
Date: 2001-12-12T02:43:22+09:00
Subject: [ruby-talk:28252] Re: Hash.keys Q

>  Yes, the order of the keys in an Hash depend of the hash function. For
>  example in your case, the order is given by

The order of the keys does not depend on the hash function -
however for small hashes there is a statistical trend. I get
the output 

order reversal occurred 484 out of 100000 times
order reversal occurred 0 out of 100000 times

when I run the following script

-----------
class Reversal
def self.count1 m
    normal = 0
    reverse = 0
    m.times do |i|
      e = new
      o = new
      hsh      = {e => o, o => e}
      swap_hsh = {o => e, e => o}
      if (hsh.keys == swap_hsh.keys)
        normal+=1
      else
        reverse+=1
      end
   end
   puts "order reversal occurred #{reverse} out of #{m} times"
end
def self.count2 m
    normal = 0
    reverse = 0
    e = new
    o = new
    m.times do |i|  
      hsh      = {e => o, o => e}
      swap_hsh = {o => e, e => o}
      if (hsh.keys == swap_hsh.keys)
        normal+=1
      else
        reverse+=1
      end
   end
   puts "order reversal occurred #{reverse} out of #{m} times"
end
end

Reversal.count1  10**5
Reversal.count2  10**5
-----------

/Christoph