Cumulative standard deviation: Difference between revisions

===Using global variables===

sdN += 1

sdSum += x

sqrt(sdSum2 / sdN - sdSum * sdSum / (sdN * sdN))

for value in [float 2,4,4,4,5,5,7,9]:

echo value, " ", formatFloat(sd(value), precision = -1)</lang>

<pre>2 0

===Using an accumulator object===

<lang Nim>import math, strutils

type SDAccum = object

sdN, sdSum, sdSum2: float

var accum: SDAccum

proc add(accum: var SDAccum; value: float): float =

# Add a value to the accumulator. Return the standard deviation.

accum.sdN += 1

accum.sdSum += value

accum.sdSum2 += value * value

result = sqrt(accum.sdSum2 / accum.sdN - accum.sdSum * accum.sdSum / (accum.sdN * accum.sdN))

for value in [float 2, 4, 4, 4, 5, 5, 7, 9]:

echo value, " ", formatFloat(accum.add(value), precision = -1)</lang>

{{out}}

Same output.

===Using a closure===

<lang Nim>import math, strutils

func accumBuilder(): auto =

var sdSum, sdSum2, sdN = 0.0

result = func(value: float): float =

sdN += 1

sdSum += value

sdSum2 += value * value

result = sqrt(sdSum2 / sdN - sdSum * sdSum / (sdN * sdN))

let std = accumBuilder()

for value in [float 2, 4, 4, 4, 5, 5, 7, 9]:

echo value, " ", formatFloat(std(value), precision = -1)</lang>

{{out}}

Same output.