Set of basic statistic operations

stat_basic.py

# Set of basic statistics operations
#

import math


def median(items):
    """
    Return median
    if number of items is odd, return average of 2 middles.

    >>> items = [10, 2, 5, 7, 4]
    >>> median(items)
    4
    """
    num_items = len(items)
    if num_items % 2 == 0:
        return items[num_items - 1]
    else:
        m1 = items[int(num_items)]
        m2 = items[int(num_items) + 1]
        return (m1 + m2) / 2

def arithmetic_mean(items):
    """
    Return arithmetic mean

    >>> items = [10, 2, 5, 7, 4]
    >>> arithmetic_mean(items)
    5.6
    """
    return reduce(lambda x, y: x + y, items) / float(len(items))

def sum_of_squares_deviation(items):
    """
    Return sum of squares deviation

    >>> items = [10, 2, 5, 7, 4]
    >>> sum_of_squares_deviation(items)
    37.2
    """
    ave_items = arithmetic_mean(items)
    deviation_of_items = map(lambda x: pow(x - ave_items, 2), items)
    return reduce(lambda x, y: x + y, deviation_of_items)

def divergence(items):
    """
    Return divergence

    >>> items = [10, 2, 5, 7, 4]
    >>> divergence(items)
    9.3
    """
    return sum_of_squares_deviation(items) / (len(items) - 1)

def standard_deviation(items):
    """
    Return standard deviation

    >>> items = [10, 2, 5, 7, 4]
    >>> round(standard_deviation(items), 2)
    3.05
    """
    return math.sqrt(divergence(items))