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NumPy - delete() function



The NumPy delete() function returns a new array with sub-arrays along an axis deleted. For a one dimensional array, this returns those entries not returned by arr[obj].

Syntax

numpy.delete(arr, obj, axis=None)

Parameters

arr Required. Specify the input array (array_like).
obj Required. Specify indices of sub-arrays to remove along the specified axis. It can be slice, int or array of ints.
axis Optional. Specify the axis along which to delete the subarray defined by obj. If axis is None, obj is applied to the flattened array.

Return Value

Returns a copy of arr with the elements specified by obj removed..

Example:

In the example below, delete() function is used to delete a given object from an array.

import numpy as np

Arr = np.array([[10, 20, 30],
                [40, 50, 60],
                [70, 80, 90]])

#deleteing 3rd element (axis=None)
Arr1 = np.delete(Arr, 2)

#deleteing 2nd row
Arr2 = np.delete(Arr, 1, 0)

#deleteing 2nd column
Arr3 = np.delete(Arr, 1, 1)

#displaying results
print("Arr is:")
print(Arr)
print("\nArr1 is (delete with axis=None):")
print(Arr1)
print("\nArr2 is (delete with axis=0):")
print(Arr2)
print("\nArr3 is (delete with axis=1):")
print(Arr3)

The output of the above code will be:

Arr is:
[[10 20 30]
 [40 50 60]
 [70 80 90]]

Arr1 is (delete with axis=None):
[10 20 40 50 60 70 80 90]

Arr2 is (delete with axis=0):
[[10 20 30]
 [70 80 90]]

Arr3 is (delete with axis=1):
[[10 30]
 [40 60]
 [70 90]]

Example:

In the example below, delete() function is used to delete a number of rows/columns from an array.

import numpy as np

Arr = np.array([[1, 2, 3, 4],
                [5, 6, 7, 8],
                [9, 10, 11, 12],
                [13, 14, 15, 16]])

#deleteing 2nd and 3rd rows
Arr1 = np.delete(Arr, [1, 2], axis=0)

#deleteing 2nd and 3rd columns
Arr2 = np.delete(Arr, [1, 2], axis=1)

#displaying results
print("Arr is:")
print(Arr)
print("\nArr1 is (delete with axis=0):")
print(Arr1)
print("\nArr2 is (delete with axis=1):")
print(Arr2)

The output of the above code will be:

Arr is:
[[ 1  2  3  4]
 [ 5  6  7  8]
 [ 9 10 11 12]
 [13 14 15 16]]

Arr1 is (delete with axis=0):
[[ 1  2  3  4]
 [13 14 15 16]]

Arr2 is (delete with axis=1):
[[ 1  4]
 [ 5  8]
 [ 9 12]
 [13 16]]

Example:

Similary a slice() function can be used to specify rows/columns to delete from an array.

import numpy as np

Arr = np.array([[1, 2, 3, 4],
                [5, 6, 7, 8],
                [9, 10, 11, 12],
                [13, 14, 15, 16]])

#deleteing alternate rows
Arr1 = np.delete(Arr, slice(None, None, 2), axis=0)

#deleteing alternate columns
Arr2 = np.delete(Arr, slice(None, None, 2), axis=1)

#displaying results
print("Arr is:")
print(Arr)
print("\nArr1 is (delete with axis=0):")
print(Arr1)
print("\nArr2 is (delete with axis=1):")
print(Arr2)

The output of the above code will be:

Arr is:
[[ 1  2  3  4]
 [ 5  6  7  8]
 [ 9 10 11 12]
 [13 14 15 16]]

Arr1 is (delete with axis=0):
[[ 5  6  7  8]
 [13 14 15 16]]

Arr2 is (delete with axis=1):
[[ 2  4]
 [ 6  8]
 [10 12]
 [14 16]]

❮ NumPy - Array Manipulation

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