时间戳

首页 > 解决方案 > 从现有列表创建新数组

python - 从现有列表创建新数组

问题描述

我有一个给定的数组，我想从第一个值开始获取每个第三个值并将其附加到一个新列表中。我可以取我想要的值，但它以1 x 28数组的形式返回。我希望它作为4 x 7数组返回。我怎么能告诉它当它到达第一行的末尾时开始新的一行？

代码：

import numpy as np

list = [
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20],
    [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21],
    [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22],
    [4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23]
]
newlist = []
list = np.array(list)
for row in list:
    k = 0
    for value in row:
        if k % 3 == 0:
            newlist.append(value)
        else:
            pass
        k += 1
newlist = np.array(newlist)
print(newlist)

输出：

[ 1  4  7 10 13 16 19  2  5  8 11 14 17 20  3  6  9 12 15 18 21  4  7 10 13 16 19 22]

期望的输出：

[[ 1  4  7 10 13 16 19 ][ 2  5  8 11 14 17 20 ][ 3  6  9 12 15 18 21 ][ 4  7 10 13 16 19 22]]

标签： pythonarrayslistnumpyappend

解决方案

尝试使用::3带有列表理解的切片：

l = [
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20],
    [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21],
    [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22],
    [4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23]
]
print(np.array([i[::3] for i in l]))

要了解有关切片的更多信息，请查看此处：

理解切片符号

推荐阅读