swapping 2 terms in a numpy array, python

Question

import numpy as np

old_order=np.array([0,1,2,3,4,5,6,7,8])
new_order=old_order
swap_1,swap_2=random.sample(range(0,9),2)
new_order[swap_1],new_order[swap_2]=old_order[swap_2],old_order[swap_1]

print(old_order,new_order)

So I am trying to swap two random element within an array. old_order would be the original array and new_order would be the array after the switch happened. What I don't understand is that why would the values of the old_order be changed

enter image description here

I have narrow down the problem to

new_order[swap_1],new_order[swap_2]=old_order[swap_2],old_order[swap_1]

If this line is remove, both new order and old order will be the same.

Tim Roberts · Accepted Answer · 2021-04-19 05:12:13Z

2

There is only one array. old_order and new_order are both bound to the same array. This line

new_array = old_array

makes a new reference. It doesn't make a copy of the data. If you really need a copy, use old_order.copy().

answered Apr 19, 2021 at 5:12

Tim Roberts

55.3k4 gold badges28 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Tony Yu Over a year ago

Thank you so much, I have been scratching my head for like an hour

ZheLiu · Accepted Answer · 2021-04-19 05:13:30Z

0

new_order=old_order.copy()

Create a new array for new_order. Otherwise new_order, old_order take the same memory.

answered Apr 19, 2021 at 5:13

ZheLiu

33 bronze badges

Collectives™ on Stack Overflow

swapping 2 terms in a numpy array, python

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related