Lets say we have a numpy array:
A = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9],
[10, 11, 12]])
Can anyone explain why this line is used to swap two rows(in this occasion the 1st with the 4th)?
'A[[0, 3]] = A [[3, 0]]'
You are updating the positions of two subarrays simultaneously.
However, doing:
A[0] = A[3]
A[3] = A[0]
would not work because the subarray A[0] has already been updated, so you need to do it simultaneously with:
A[[0, 3]] = A [[3, 0]]
A
array([[10, 11, 12],
[ 4, 5, 6],
[ 7, 8, 9],
[ 1, 2, 3]])