Modify numpy array of arrays

Question

I have a numpy array of numpy arrays and I need to add a leading zero to each of the inner arrays:

a = [[1 2] [3 4] [5 6]] --> b = [[0 1 2] [0 3 4] [0 5 6]]

Looping through like this:

for item in a:

item = np.insert(item, 0, 0)

doesn't help.

Numpy.put() flattens the array, which I don't want.

Any suggestions how I accomplish this? Thanks

You can also use np.hstack, but np.insert answered below is more effectient — oppressionslayer
– oppressionslayer, Commented Nov 1, 2024 at 1:20
This question is similar to: Numpy add (append) value to each row of 2-d array. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. — Anerdw
– Anerdw, Commented Nov 1, 2024 at 1:22
I'm not sure how good that dupe target is, but I wanted to throw it out there. — Anerdw
– Anerdw, Commented Nov 1, 2024 at 1:22

Konstantin Makarov · Accepted Answer · 2024-11-01 00:01:49Z

4

np.insert - insert values along the given axis before the given indices. If axis is None then array is flattened first.

import numpy as np

a = np.array([[1, 2], [3, 4], [5, 6]])
b = np.insert(a, 0, 0, axis=1)
print(b)

Result:

[[0 1 2]
 [0 3 4]
 [0 5 6]]

answered Oct 31, 2024 at 23:45

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