得到一个numpy数组的对角线 [英] getting the opposite diagonal of a numpy array
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问题描述
因此在numpy数组中,有用于获取对角线索引的内置函数,但是我似乎无法弄清楚如何从右上角而不是左上角开始获取对角线.
So in numpy arrays there is the built in function for getting the diagonal indices, but I can't seem to figure out how to get the diagonal starting from the top right rather than top left.
这是从左上角开始的普通代码:
This is the normal code to get starting from the top left:
>>> import numpy as np
>>> array = np.arange(25).reshape(5,5)
>>> diagonal = np.diag_indices(5)
>>> array
array([[ 0, 1, 2, 3, 4],
[ 5, 6, 7, 8, 9],
[10, 11, 12, 13, 14],
[15, 16, 17, 18, 19],
[20, 21, 22, 23, 24]])
>>> array[diagonal]
array([ 0, 6, 12, 18, 24])
所以如果我希望它返回,该怎么办?
so what do I use if I want it to return:
array([ 4, 8, 12, 16, 20])
推荐答案
有
In [47]: np.diag(np.fliplr(array))
Out[47]: array([ 4, 8, 12, 16, 20])
或
In [48]: np.diag(np.rot90(array))
Out[48]: array([ 4, 8, 12, 16, 20])
两者中的np.diag(np.fliplr(array))
更快:
In [50]: %timeit np.diag(np.fliplr(array))
100000 loops, best of 3: 4.29 us per loop
In [51]: %timeit np.diag(np.rot90(array))
100000 loops, best of 3: 6.09 us per loop
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