argsort 在numpy和torch中

默认是升序排列，调用ndarray.argsort 或者 tensor.argsort 返回的是index，加负号，将index逆序即可得到降序。

import torch
import numpy as np

if __name__ == '__main__':

    b = np.array([[2,3,4,5],
                  [5,6,7,8],
                  [2,2,2,2]])
    # increasing order by default
    order = b[:,3].argsort()
    print(order)
    # descend
    c = b[-order]
    print(c)
    # increase
    d = b[order]
    print(d)
    a = torch.tensor([[2,3,4,5],
                  [5,6,7,8],
                  [2,2,2,2]])
    order = a[:,3].argsort()
    print(order)
    e = a[-order]
    print(e)

[2 0 1]
[[5 6 7 8]
 [2 3 4 5]
 [2 2 2 2]]
[[2 2 2 2]
 [2 3 4 5]
 [5 6 7 8]]
tensor([2, 0, 1])
tensor([[5, 6, 7, 8],
        [2, 3, 4, 5],
        [2, 2, 2, 2]])