Source code for simplestatistics.statistics.variance

# I need sane division that returns a float not int
from __future__ import division

from .mean import mean
from .decimalize import decimalize

[docs]def variance(data, sample = True): """ Variance_ is the sum of squared deviations from the mean. It is a general measurement of how far from the mean the values are. .. _Variance: http://en.wikipedia.org/wiki/Variance Args: data: A list of numeric objects. sample: A boolean value. If True, calculates sample variance. If False, calculates population variance. Returns: A float object. Examples: >>> variance([1, 2, 3, 4]) 1.6666666666666667 >>> variance([1, 2, 3, 4], sample = False) 1.25 >>> variance([1, 2, 3, 4, 5, 6]) 3.5 >>> variance([-2, -1, 0, 1, 2]) 2.5 >>> variance([1]) # variance of one value is not defined >>> variance([4]) # variance of one value is not defined """ if len(data) < 2: return(None) data = decimalize(data) m = decimalize(mean(data)) if sample: return(float(sum([pow(x - m, 2) for x in data]) / (len(data) - 1))) else: return(float(mean([pow(x - m, 2) for x in data])))