如何将一个数组的多行和多列分配给 Python 中另一个数组的相同行和列？

Question

As the title says, how do I assign multiple rows and columns of one array to the same rows and columns of another array in Python?

I want to do the following:

 Kn[0, 0] = KeTrans[startPosRow, startPosCol];
 Kn[0, 1] = KeTrans[startPosRow, endPosCol];
 Kn[1, 0] = KeTrans[endPosRow, startPosCol];
 Kn[1, 1] = KeTrans[endPosRow, endPosCol];

Kn is a 2X2 matrix and KeTrans is a 4X4.

I tried the following but with no luck.

Kn[0:1, 0:1] = KeTrans[startPosRow: endPosRow, startPosCol: endPosCol]

Answer 1

For multi-dimensional arrays, I highly suggest use Numpy.

import numpy as np

To create an Nth-dimensional array:

a = np.array([4,2,4],[23,4,3,2]...,[2,3,4])

The array are indexed very intuitively:

>> a[0,1]
4

You can even do slicing for the np array.

documentation of numpy multi-dimensional array: https://numpy.org/doc/stable/reference/arrays.ndarray.html

Answer 2

But they're not the same rows and columns:-) (unless startPosRow and friends have very specific values).

The problem is that the slice startPosRow:endPosRow (for example) does not mean "element startPosRow and element endPosRow ". It means "elements in range(startPosRow, endPosRow) ", which doesn't include endPosRow and which typically has more than two matching indices.

If you just want the four corners, you could use slices with a step size:

Kn[0:1, 0:1] = KeTrans[startPosRow:endPosRow + 1:endPosRow - startPosRow,
                       startPosCol:endPosCol + 1:endPosCol - startPosCol]

Answer 3

Is this what you are trying to do:

In [323]: X = np.arange(16).reshape(4,4)
In [324]: Y = np.zeros((2,2),int)
In [325]: Y[:] = X[:2,:2]
In [326]: Y
Out[326]: 
array([[0, 1],
       [4, 5]])
In [327]: Y[:] = X[1:3,2:]
In [328]: Y
Out[328]: 
array([[ 6,  7],
       [10, 11]])

For reference

In [329]: X
Out[329]: 
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11],
       [12, 13, 14, 15]])