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Python Introduction to NumPy Array Organization Slicing

Posted by Victor Adukwu
Victor Adukwu
1,379 Points

I modified a slice of ndarray and this also modified the original array. Why is it contrary to what we see in the video?

In the video, modifying the copied array did not change the fruits array. When I practice modifying a slice of an array, the original array was modified. In addition, answering one of the quiz questions based on the video will give a wrong answer. Is there something I am missing?

Cheo R
Cheo R
37,150 Points
Cheo R
Cheo R
37,150 Points

Can you post your code?

Victor Adukwu
Victor Adukwu
1,379 Points 
fruits = np.array(['orange', 'guava', 'grape'])
copied = fruits[1:]
copied[0] = 'berry'
fruits, copied

Output:

(array(['orange', 'berry', 'grape'], dtype='<U6'),
 array(['berry', 'grape'], dtype='<U6'))
Cheo R
Cheo R
37,150 Points
Cheo R
Cheo R
37,150 Points

It looks like you're returning a view and not a copy. Rewatch the video starting at 8:10 where he explains the difference.

1 Answer

paul nabende
paul nabende
673 Points

When you say that

In the video, modifying the copied array did not change the fruits array.

you are probably referring to the time around minute 04:14. Note that in that case, it was a list. Slicing a list will return a copy but slicing an ndarray as explained around minute 8:13 will return only a view.

If you were testing out slicing lists, the proper command should have been 

fruits = ['orange', 'guava', 'grape']
copied = fruits[1:]
copied[0] = 'berry'
fruits, copied

To get the desired output

(['orange', 'guava', 'grape'], ['berry', 'grape'])