如何计算到 pandas 系列中前一个零的距离? [英] How to count distance to the previous zero in pandas series?

问题描述

我有以下熊猫系列(以列表形式表示):

I have the following pandas series (represented as a list):

[7,2,0,3,4,2,5,0,3,4]

我想定义一个新的序列，该序列返回到最后一个零的距离.这意味着我希望获得以下输出:

I would like to define a new series that returns distance to the last zero. It means that I would like to have the following output:

[1,2,0,1,2,3,4,0,1,2]

如何以最有效的方式在熊猫中做到这一点?

How to do it in pandas in the most efficient way?

推荐答案

复杂度为O(n).减慢速度的是在python中执行for循环.如果序列中有k个零，并且与序列的长度相比log k是可忽略的，则O(n log k)解决方案将是:

The complexity is O(n). What will slow it down is doing a for loop in python. If there are k zeros in the series, and log k is negligibile comparing to the length of series, an O(n log k) solution would be:

>>> izero = np.r_[-1, (ts == 0).nonzero()[0]]  # indices of zeros
>>> idx = np.arange(len(ts))
>>> idx - izero[np.searchsorted(izero - 1, idx) - 1]
array([1, 2, 0, 1, 2, 3, 4, 0, 1, 2])

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