From: Maarten Boonen <m44rt3n@...>
Date: 2004-12-16T17:32:13+09:00
Subject: Re: [ANN] rand.rb 0.9: Random access methods for Enumerables

nobu.nokada@softhome.net schreef:
> Hi,
> 
> At Thu, 16 Dec 2004 07:12:15 +0900,
> Maarten Boonen wrote in [ruby-talk:123730]:
> 
>>I made this a function a few days ago and it seems to be a lot faster. 
>>Not sure if it's completely correct though.
>>
>>def shuffle!
>>	a = 0
>>	while(a<length)
>>		b = (length*Kernel.rand).to_i
>>		tmp = self[a]
>>		self[a] = self[b]
>>		self[b] = tmp
>>		a+=1
>>	end
>>	self
>>end
> 
> 
> It wouldn't be uniform.  An element which was close to the head
> will tend to be placed close to the tail.
> 

I tested this, by shuffeling an array [1..10] 100000 times and the 
elements at the head seem to be smaller (closer to the head again)?


 >ruby test2.rb
512468
528318
540408
550876
559504
566140
567602
565901
559436
549347
 >Exit code: 0
 >ruby test2.rb
512626
527151
539146
551026
560751
565943
565926
566866
560561
550004
 >Exit code: 0
 >ruby test2.rb
511651
526778
541792
551417
559825
563856
567336
566272
561004
550069
 >Exit code: 0




class Array

def shuffle!
	a = 0
	while(a<length)
		b = (length*Kernel.rand).to_i
		tmp = self[a]
		self[a] = self[b]
		self[b] = tmp
		a+=1
	end
	self
end

end


total = Array.new(10,0)
for i in 1..100000
	arr = (1..10).to_a
	arr.shuffle!
	total.each_index do |index| total[index] += arr[index] end
end

puts total