单次通过计算发电机的统计数据.蟒蛇

Question

使用生成器时,您只能在一次通过时拉出项目.另一种方法是将生成器加载到列表中并执行多次传递,但这会影响性能和内存分配.

任何人都可以想到一种更好的方法,可以在一次通过中从生成器计算以下指标.理想情况下,代码计算您可以想到的计数,总和,平均值,标准差,最大值,最小值和任何其他统计数据.

UPDATE

这个要点中最初的可怕代码.请参阅此处的要点:https://gist.github.com/3038746

使用来自@larsmans的伟大建议是我最后的解决方案.使用命名元组确实有帮助.

import random
from math import sqrt
from collections import namedtuple

def stat(gen):
    """Returns the namedtuple Stat as below."""
    Stat = namedtuple('Stat', 'total, sum, avg, sd, max, min')
    it = iter(gen)

    x0 = next(it)
    mx = mn = s = x0
    s2 = x0*x0
    n = 1

    for x in it:
        mx = max(mx, x)
        mn = min(mn, x)
        s += x
        s2 += x*x
        n += 1

    return Stat(n, s, s/n, sqrt(s2/n - s*s/n/n), mx, mn)

def random_int_list(size=100, start=0, end=1000):
    return (random.randrange(start,end,1) for x in xrange(size))

if __name__ == '__main__':
    r = stat(random_int_list())
    print r  #Stat(total=100, sum=56295, avg=562, sd=294.82537204250247, max=994, min=10)

Answer 1

def statistics(it):
    """Returns number of elements, sum, max, min"""

    it = iter(it)

    x0 = next(it)
    maximum = minimum = total = x0
    n = 1

    for x in it:
        maximum = max(maximum, x)
        minimum = min(minimum, x)
        total += x
        n += 1

    return n, total, maximum, minimum

随便添加其他统计信息.namedtuple当计算的统计数量增长时,请考虑使用a .

如果你想变得非常花哨,你可以构建统计收集器的OO层次结构(未经测试):

class Summer(object):
    def __init__(self, x0=0):
        self.value = x0

    def add(self, x):
        self.value += x

class SquareSummer(Summer):
    def add(self, x):
        super(SquareSummer, self).add(x ** 2)

class Maxer(object):
    def __init__(self, x0):
        self.value = x0

    def add(self, x):
        self.value = max(self.value, x)

# example usage: collect([Maxer, Summer], iterable)
def collect(collectors, it):
    it = iter(it)

    x0 = next(it)
    collectors = [c(x0) for c in collectors]

    for x in it:
        for c in collectors:
            c.add(x)

    return [c.value for c in collectors]