Accessing elements of an array from one given index to another given index is known as slicing in python.

Instead of passing index, we pass slice with step –

[start:end:step]

If we don’t pass start its considered 0

If we don’t pass end its considered length of array in that dimension

If we don’t pass step its considered 1

Example-

import numpy as np

arr = np.array([1, 2, 3, 4, 5, 6])

print(arr[1:3])
print(arr[3:]) 
print(arr[:3])
print(arr[-3:-1])
print(arr[1:4:2])
print(arr[::2])

Output–

[2 3]
[4 5 6]
[1 2 3]
[4 5]
[2 4]
[1 3 5]

Explanation-

arr[1:3] – Slice elements from index 1 to index 3 from the array arr. The result is – [2 3], which includes the value available at start index 1, but excludes the end index 3.

arr[3: ] – Slice elements from index 3 to the end of the array arr.

arr[:3] – Slice elements from the beginning to index 3(not included)

arr[-3:-1] – Slice from the index 3 from the end to index 1 from the end

arr[1:4:2] – Here step value is 2, so it will return every other element from index 1 to index 4.

arr([::2]) – Return every other element from the entire array

Slicing 2-D Arrays

import numpy as np

arr = np.array([[1, 2, 3, 4, 5], [6, 7, 8, 9, 10]])

print(arr[1, 1:3])
print(arr[0:2, 3])
print(arr[0:2, 1:3])

Output-

[7 8]
[4 9]
[[2 3]
 [7 8]]

Explanation-

arr[1, 1:3]- From the second element, slice elements from index 1 to index 3 (not included)

arr[0:2, 3]- From both elements, return index 3

arr[0:2, 1:3]- From both elements, slice index 1 to index 3(not included), this will return a 2-D array