Delete specific position from numpy array

Question

I have some numpy arrays with None in the first position.

a = [None, 1, 2, 3, 4, 5]
b = [None, 4, 3, 2, 1, 5]

I want it to become:

[1, 2, 3, 4, 5]
[4, 3, 2, 1, 5]

EDIT: I know I can do:

a = [a is not None]

But In my case I want to specifically remove a[0]

tried:

a = np.delete(a, 0)

got:

AttributeError: int' object has no attribute 'delete'

Does this answer your question? How to remove all rows in a numpy.ndarray that contain non-numeric values — Mateo Torres
– Mateo Torres, Commented Nov 17, 2020 at 18:35
arr[:, 1:] will select all but the first column. With None the array will be object dtype. Without it it could be converted to numeric dtype, as with arr[:, 1:].astype(int). — hpaulj
– hpaulj, Commented Nov 17, 2020 at 18:36
Does this answer your question? efficient way of removing None's from numpy array — Rivers
– Rivers, Commented Nov 17, 2020 at 18:36
It partly does, but this methods search the None's (O(n)). In my case, I know that it is in array[0]. There is not there a better way? — bakun
– bakun, Commented Nov 17, 2020 at 18:45
You have messed up the np variable. It no longer is the imported module. Start over! — hpaulj
– hpaulj, Commented Nov 17, 2020 at 19:21

hpaulj · Accepted Answer · 2020-11-17 19:25:29Z

2

a is a list:

In [61]: a = [None, 1,2,3,4]
In [62]: a
Out[62]: [None, 1, 2, 3, 4]
In [63]: a[1:]               # standard list slicing
Out[63]: [1, 2, 3, 4]

If we have an array, we can do the same slicing:

In [64]: A = np.array(a)
In [65]: A
Out[65]: array([None, 1, 2, 3, 4], dtype=object)
In [66]: A[1:]
Out[66]: array([1, 2, 3, 4], dtype=object)
In [67]: A[1:].astype(int)
Out[67]: array([1, 2, 3, 4])

With None the array is object dtype, similar to a list.

With the list, we can also us del (and remove any selected item):

In [68]: a
Out[68]: [None, 1, 2, 3, 4]
In [69]: del a[0]
In [70]: a
Out[70]: [1, 2, 3, 4]

np.delete does something similar for an array, though it isn't as efficient:

In [72]: np.delete(A, 0)
Out[72]: array([1, 2, 3, 4], dtype=object)

If np.delete doesn't work for you, it's because you've messed up np.

answered Nov 17, 2020 at 19:25

hpaulj

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bakun Over a year ago

Slicing solved it! As for np.delete, it worked when I tested it on some random array, but for some reason it is not working in my program's array.. anyway ty!

sushanth · Accepted Answer · 2020-11-17 18:41:14Z

0

Numpy just have a beautiful method. Use .delete()

Example:

n = [None, 1, 2, 3, 4, 5]
n = np.delete(n, 0)

EDIT : np stands for numpy. Use: import numpy as np

edited Nov 17, 2020 at 18:41

sushanth

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answered Nov 17, 2020 at 18:37

HolySpeeddo

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1 Comment

bakun Over a year ago

AttributeError: "Int" object has no attribute 'delete'

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