编辑:
似乎来自scikits.timeseries.lib.moving_funcs子模块的mov_average_expw()
函数,来自SciKits(补充了SciPy的附加工具包),更符合您问题的措辞。
要使用平滑系数alpha
(在维基百科的术语中为(1-alpha)
)计算数据的指数平滑:
>>> alpha = 0.5
>>> assert 0 < alpha <= 1.0
>>> av = sum(alpha**n.days * iq
... for n, iq in map(lambda (day, iq), today=max(days): (today-day, iq),
... sorted(zip(days, IQ), key=lambda p: p[0], reverse=True)))
95.0
以上代码看起来不太美观,我们对其进行一些重构:
from collections import namedtuple
from operator import itemgetter
def smooth(iq_data, alpha=1, today=None):
"""Perform exponential smoothing with factor `alpha`.
Time period is a day.
Each time period the value of `iq` drops `alpha` times.
The most recent data is the most valuable one.
"""
assert 0 < alpha <= 1
if alpha == 1:
return sum(map(itemgetter(1), iq_data))
if today is None:
today = max(map(itemgetter(0), iq_data))
return sum(alpha**((today - date).days) * iq for date, iq in iq_data)
IQData = namedtuple("IQData", "date iq")
if __name__ == "__main__":
from datetime import date
days = [date(2008,1,1), date(2008,1,2), date(2008,1,7)]
IQ = [110, 105, 90]
iqdata = list(map(IQData, days, IQ))
print("\n".join(map(str, iqdata)))
print(smooth(iqdata, alpha=0.5))
示例:
$ python26 smooth.py
IQData(date=datetime.date(2008, 1, 1), iq=110)
IQData(date=datetime.date(2008, 1, 2), iq=105)
IQData(date=datetime.date(2008, 1, 7), iq=90)
95.0
sum(alpha**((today - date).days) * iq for date, iq in iq_data)
给出了指数加权和。它需要除以分母sum(alpha**((today - date).days) for date, iq in iq_data)
才能得到平均值。 - matohak