如何计算列表中数组的特定元素的出现次数？

Question

如何计算具有少量数组的列表中某个整数的出现？例如,我想查找值2的出现次数.

import numpy as np
a = [np.array([2, 2, 1, 2]), np.array([1, 3])]

预期产量:

[3, 0]

谁能帮我？

Answer 1

一种方法是使用 Counter

In [3]: from collections import Counter

给出所有数字的频率

In [4]: [Counter(x) for x in a]
Out[4]: [Counter({2: 3, 1: 1}), Counter({1: 1, 3: 1})]

只计算数量 2

In [5]: [Counter(x)[2] for x in a]
Out[5]: [3, 0]

或者,您可以使用np.bincount方法来计算非负的int数组中每个值的出现次数.

In [6]: [np.bincount(x) for x in a]
Out[6]: [array([0, 1, 3], dtype=int64), array([0, 1, 0, 1], dtype=int64)]

提取数量的计数 2

In [7]: [np.bincount(x)[2] for x in a]
Out[7]: [3, 0]