参考：https://numpy.org/doc/stable/reference/generated/numpy.ndarray.flatten.html
语法格式
ndarray.flatten(order='C')
参数order有{"C", "F', "A", "K"}可供选择。C '表示按行(C-style)；"F"表示按列(Fortran-style)。默认值是"C"。
代码示例
import numpy as np
x=np.zeros((5,4))
x[:,range(3)]=1
print(x)
print(x.flatten()) #按行
print(x.flatten("F")) #按列输出结果
[[1. 1. 1. 0.]
[1. 1. 1. 0.]
[1. 1. 1. 0.]
[1. 1. 1. 0.]
[1. 1. 1. 0.]]
[1. 1. 1. 0. 1. 1. 1. 0. 1. 1. 1. 0. 1. 1. 1. 0. 1. 1. 1. 0.]
[1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 0. 0. 0. 0. 0.]