给定行和列索引，分配到NumPy数组的网格中

问题描述：

我想访问2d numpy数组的特定行和列限制.

I want to access a specific row and column restriction of a 2d numpy array.

> x
array([[1, 2, 0],
       [3, 4, 0],
       [0, 0, 1]])

如果我做自然的事情，我只会得到受限数组的对角线元素.

If I do what seems natural, I just get the diagonal elements of the restricted array.

> x[[0,1], [0,1]]
array([1, 4])

相反，我可以这样做来阅读我想要的内容-

Instead I can do this to read what I want -

> x[[0,1],:][:,[0,1]]
array([[1, 2],
       [3, 4]])

..但是它不允许我编写/分配值.

..but it doesn't let me write/assign the values.

> x[[0,1],:][:,[0,1]] = np.array([[1,0],[0,1]])

> x 
array([[1, 2, 0],
       [3, 4, 0],
       [0, 0, 1]])

如何在此处写入矩阵?

答

使用

Use np.ix_ to map that grid of elements and then assign -

x[np.ix_([0,1], [0,1])] = np.array([[1,0],[0,1]])