Python numpy数组对某些索引求和 [英] Python numpy array sum over certain indices

问题描述

如何仅对 numpy 数组上的索引列表执行求和，例如，如果我有一个数组 a = [1,2,3,4] 和要求和的索引列表, indices = [0, 2] 我想要一个快速的操作来给我答案 4 因为在 中索引 0 和索引 2 处的值求和的值a 是 4

How to perform a sum just for a list of indices over numpy array, e.g., if I have an array a = [1,2,3,4] and a list of indices to sum, indices = [0, 2] and I want a fast operation to give me the answer 4 because the value for summing value at index 0 and index 2 in a is 4

推荐答案

用indices索引后可以直接使用sum:

You can use sum directly after indexing with indices:

a = np.array([1,2,3,4])
indices = [0, 2] 
a[indices].sum()

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