Created
July 26, 2014 23:06
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これだと偏る
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#! /usr/bin/env ruby | |
require 'pp' | |
def shuffle(array) | |
i = array.length | |
while 0 < i | |
i = i - 1 | |
j = (Random.rand * i).to_i | |
array[i], array[j] = array[j], array[i] | |
end | |
array | |
end | |
N = 10 | |
M = 10_000 | |
sum_array = Array.new(N, 0) | |
M.times do | |
ret = shuffle((1..N).to_a) | |
sum_array = sum_array.zip(ret).map { |x,y| x+y} | |
end | |
avg = ((1 + N) * N / 2).to_f / N | |
sum_array.map! {|n| n.to_f / M / avg} | |
pp sum_array | |
__END__ | |
[1.0824181818181817, | |
1.0727454545454547, | |
1.0495818181818182, | |
1.0350727272727271, | |
1.0113454545454545, | |
0.9922727272727272, | |
0.9672727272727273, | |
0.9484727272727272, | |
0.9301636363636363, | |
0.9106545454545455] |
#! /usr/bin/env ruby
require 'pp'
def shuffle(array)
i = array.length
while 1 < i
i = i - 1
j = (Random.rand * (i+1)).to_i
array[i], array[j] = array[j], array[i]
end
array
end
N = 10
M = 10_000
sum_array = Array.new(N, 0)
M.times do
ret = shuffle((1..N).to_a)
sum_array = sum_array.zip(ret).map { |x,y| x+y}
end
avg = ((1 + N) * N / 2).to_f / N
sum_array.map! {|n| n.to_f / M / avg}
pp sum_array
__END__
[0.9967636363636363,
0.9968,
1.0102363636363636,
0.9960181818181819,
0.9953454545454545,
1.0029272727272727,
1.0000909090909091,
0.9993090909090909,
1.0014727272727273,
1.0010363636363637]
while loop も一回少なくできる
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j = (Random.rand * (i + 1)).to_i
であるべきなのかな