我有 3d 数组 m*n*k
,对于每个 2d 层,我想获取一个大小为 i*j
的子数组。我有一个数组 c,其大小为每层切片起始坐标的 2*k
。有没有好的简单方法可以在没有任何循环的情况下获得我需要的东西?
示例:
test = np.arange(18).reshape((3,3,2))
c = np.array([[0,1], [0, 1]])
test[:,:,0] = array([[ 0, 2, 4],
[ 6, 8, 10],
[12, 14, 16]])
test[:,:,1] = array([[ 1, 3, 5],
[ 7, 9, 11],
[13, 15, 17]])
我想要一个数组
[[[ 0, 9],
[ 2, 11]],
[[ 6, 15],
[ 8, 17]]]
带循环的解决方案:
h=2
w=2
layers = 2
F = np.zeros((h,w,layers))
for k in range(layers):
F[:,:,k] = test[c[0,k]:c[0,k]+h, c[1,k]:c[1,k]+w, k]
最佳答案
这是利用 broadcasting
的矢量化方法和 advanced-indexing
-
d0,d1,d2 = np.ogrid[:h,:w,:layers]
out = test[d0+c[0],d1+c[1],d2]
示例运行 -
In [112]: test = np.arange(200).reshape((10,10,2))
...: c = np.array([[0,1], [0, 1]])
...:
In [113]: h=4
...: w=5
...: layers = 2
...: F = np.zeros((h,w,layers))
...: for k in range(layers):
...: F[:,:,k] = test[c[0,k]:c[0,k]+h, c[1,k]:c[1,k]+w, k]
...:
In [114]: d0,d1,d2 = np.ogrid[:h,:w,:layers]
...: out = test[d0+c[0],d1+c[1],d2]
...:
In [115]: np.allclose(F, out)
Out[115]: True
关于python - numpy,数组不同层的不同切片,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41698626/