python - Numpy：将最后一个轴转换为列表

Question

让 numpy 数组为形状 (x, y, z)。我希望它是 (x, y) 形状，每个元素都是 z 长度的列表：[a, b, c, ..., z] 有没有办法用 numpy 方法来做到这一点？

标签： pythonlistnumpy

Answer 1

您可以使用tolist并分配给预分配的对象数组：

import numpy as np

a = np.random.randint(0,10,(100,100,100))

def f():
    A = np.empty(a.shape[:-1],object)
    A[...] = a.tolist()
    return A

f()[99,99]
# [4, 5, 9, 2, 8, 9, 9, 6, 8, 5, 7, 9, 8, 7, 6, 1, 9, 6, 2, 9, 0, 7, 0, 1, 2, 8, 4, 4, 7, 0, 1, 2, 3, 8, 9, 6, 0, 1, 4, 7, 0, 7, 9, 3, 9, 1, 8, 7, 1, 2, 3, 6, 6, 2, 7, 0, 2, 8, 7, 0, 0, 1, 8, 2, 6, 3, 5, 4, 9, 6, 9, 0, 2, 5, 9, 5, 3, 7, 0, 1, 9, 0, 8, 2, 0, 7, 3, 6, 9, 9, 4, 4, 3, 8, 4, 7, 4, 2, 1, 8]
type(f()[99,99])
# <class 'list'>

from timeit import timeit
timeit(f,number=100)*10
# 28.67872992530465