NumPy: Slicing

Slicing

• Slicing means accessing a sub‒part of an array(a range of elements).

Syntax

array[start: end: step]

where

start: Index where slice begins.

end: Index where slice ends.

step: How many elements to skip

Following python programs illustrate the use of slicing in NumPy.

Python program for slicing a one D array

import numpy as np

arr = np.array([10,20,30,40,50,60])

print("Displaying slice(elements from 1 to 3)")

print(arr[1:4])

print("Displaying first three elements as slice")

print(arr[:3])

print("Displaying every alternate element as slice")

print(arr[::2])

Output

Displaying slice (elements from 1 to 3)

[20 30 40]

Displaying first three elements as slice

[10 20 30]

Displaying every alternate element as slice

[10 30 50]

The working of above code can be illustrated by following figure ‒

Python program for slicing a two D array

import numpy as np

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

[5,6,7,8],

[9,10,11,12],

 [13,14,15,16]])

print("Slice second and third rows and first three columns")

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

Output

slice second and third rows and first three columns

 [[ 5 6 7]

[ 9 10 11]]

Following figure illustrates how to slice a two dimensional array ‒