CODEWITHSUNDEEP
pythonnumpy
lbrice1
lbrice1

Reputation: 21

How can I get an array which is a modification of another whilst keeping the original?

I want to create two arrays a and b, then create an array c which is the same as a but the first column is pulled from b. At the end there should be 3 different arrays.

Something like the following:

a = np.array([[1, 1]])
b = np.array([[0, 0]])

c = b
c[:, 0] = a[:, 0]

print(a, b, c)

Should outputs:

[[1 1]] [[0 0]] [[1 0]]

But I am getting:

[[1 1]] [[1 0]] [[1 0]]

For some reason, modifying c also modifies a.

Upvotes: 2

Views: 46

Answers (1)

Michael Hawkins
Michael Hawkins

Reputation: 2873

You can perform a copy of the object by using .copy() like so:

a = np.array([[1, 1]])
b = np.array([[0, 0]])

c = b.copy() # or b.deepcopy()

From the documentation:

Assignment statements in Python do not copy objects, they create bindings between a target and an object. For collections that are mutable or contain mutable items, a copy is sometimes needed so one can change one copy without changing the other. [The copy] module provides generic shallow and deep copy operations...

Link: https://docs.python.org/3.8/library/copy.html

Upvotes: 3

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