NumPy (python)matrix column copying isn't working

Question

So I'm currently learning python and numpy and I'm testing this code because I can't get A[:, 1] = arr[:, 0] to work whatsoever. I thought it was maybe an object thing or something (coming from javascript/java/C to python) but it seems it's actually the arr[:, 0] that is causing issues saying that there is too many indices... but I'm just printing all of the indices in column 1 right? Lost Here.

import numpy as np

arr = np.array([1, 2, 3, 4])
degree = 7
A = np.ones((len(arr), degree))
print(A[:, 1])
print(arr[:, 0])

^ full attached code above

What is the expected output? arr is one dimensional so you can't give it two dimensional indices. — QWERTYL
– QWERTYL, Commented Apr 14, 2022 at 1:05

Kraigolas · Accepted Answer · 2022-04-14 01:04:51Z

1

For a numpy array, the number of indices cannot exceed the number of dimensions. Thus for a 1D array, giving two indices (:, 0 is two indices) is invalid, which is why you observe this error for arr but not for A.

arr[0] would give you the first element of arr, or just arr gives you the entire array.

answered Apr 14, 2022 at 1:04

Kraigolas

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