How can I change element of numpy array manually?

Question

Following is my numpy array.

import numpy as np

arr = np.array([1,2,3,4,5])
arrc=arr
arrc[arr<3]=3

When I run

>>> arrc
output : array([3,3,3,4,5])

>>> arr
output : array([3,3,3,4,5])

I expected changing arrc does not affect arr. However, both array is changing. In my actual code I am changing arrc multiple times so I observe error if arrc have influence to arr. Is there any good way to fix this?

You might mean arrc = arr.copy(). Otherwise arrc and arr are references to the same array. — hilberts_drinking_problem
– hilberts_drinking_problem, Commented Nov 12, 2022 at 3:59
arrc=arr - just assigns the same object to the new variable name. It does not make a copy. This isn't just a numpy thing; it's basic Python. But with numpy you also have to know when something is a view instead of a copy. — hpaulj
– hpaulj, Commented Nov 12, 2022 at 16:31

Austin · Accepted Answer · 2022-11-12 04:08:22Z

1

You have to .copy() when you copy array values. Otherwise, it is the same reference you update with both variables.

Use:

arrc = arr.copy()

answered Nov 12, 2022 at 4:08

Austin

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Royadma · Accepted Answer · 2022-11-12 03:57:51Z

1

Simply, just index the element and set the value.

a[1,2] = "some value"

answered Nov 12, 2022 at 3:57

Royadma

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1 Comment

Kyle Over a year ago

I have to use conditions because in my actual code the array has more than 20,000 index and they are in random order.

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