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Cumulative standard deviation: Difference between revisions
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8 :> 2.0
</pre>
=={{header|Crystal}}==
{{trans|Ruby}}
===Using an object to keep state:===
<lang ruby>class StdDevAccumulator
def initialize
@n, @sum, @sum2 = 0, 0.0, 0.0
end
def <<(num)
@n += 1
@sum += num
@sum2 += num**2
Math.sqrt (@sum2 * @n - @sum**2) / @n**2
end
end
sd = StdDevAccumulator.new
i = 0
[2,4,4,4,5,5,7,9].each { |n| puts "adding #{n}: stddev of #{i+=1} samples is #{sd << n}" }</lang>
{{out}}
<pre>
adding 2: stddev of 1 samples is 0.0
adding 4: stddev of 2 samples is 1.0
adding 4: stddev of 3 samples is 0.9428090415820634
adding 4: stddev of 4 samples is 0.8660254037844386
adding 5: stddev of 5 samples is 0.9797958971132712
adding 5: stddev of 6 samples is 1.0
adding 7: stddev of 7 samples is 1.3997084244475304
adding 9: stddev of 8 samples is 2.0
</pre>
=={{header|D}}==
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