Python中reshape函数参数-1的意思？

import numpy as np
c = np.array([[1,2,3],[4,5,6]])
print('2行3列')
print(c.reshape(2,3))
print('3行2列')
print(c.reshape(3,2))
print('我也不知道几行，反正是一列')
print(c.reshape(-1,1))
print('我也不知道几列，反正是一行')
print(c.reshape(1,-1))
print('不分行列，改成一串')
print(c.reshape(-1))

输出：

参考自https://www.zhihu.com/question/52684594