def variance(collection, unbiased = True):
"""Return the variance of a collection of numbers.
Examples:
>>> variance([])
0.0
>>> variance([1])
0.0
>>> variance([1,1,1])
0.0
>>> variance([1,2,3])
1.0
>>> variance([1,2,3], unbiased = False)
0.66666666666666663
"""
if not collection:
return float(0)
m = mean(collection)
n = float(len(collection))
sq = [ pow(x-m, 2) for x in collection ]
scale = 1/n if not unbiased or n == 1 else 1/(n-1)
return scale*fsum(sq)
def mean(sequence):
"""Return the mean of an iterable numeric sequence (e.g., a list).
Examples:
>>> mean([1,2,3])
2.0
>>> mean([])
0
"""
return fsum(sequence) / len(sequence) if sequence else 0