Array Assignment

When assigning NumPy arrays, you have to take note of how arrays are assigned. Following are a number of examples to illustrate this.

Copying by Reference

Consider an array named a1:

list1 = [[1,2,3,4], [5,6,7,8]]
a1 = np.array(list1)
print(a1)
'''
[[1 2 3 4]
 [5 6 7 8]]
''' 

When you try to assign a1 to another variable, a2, a copy of the array is created:

a2 = a1    # creates a copy by reference
print(a1)
'''
[[1 2 3 4]
 [5 6 7 8]]
'''
 
print(a2)
'''
[[1 2 3 4]
 [5 6 7 8]]
''' 

However, a2 is actually pointing to the original a1. So, any changes made to either array will affect the other as follows:

a2[0][0] = 11      # make some changes to a2
print(a1)          # affects a1
'''
[[11  2  3  4]
 [ 5  6  7  8]]
'''
 
print(a2)
'''
[[11  2  3  4]
 [ 5  6  7  8]]
''' 

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TIP

In the “Reshaping Arrays” section...