Convert Python List to NumPy Arrays

Introduction

In Python, a list is a linear data structure that may store heterogeneous elements. It does not need to be defined and can shrink and expand as needed. On the other end, a NumPy array is a data structure that may store homogenous elements. It is implemented in Python using the NumPy library. This library is very efficient in handling multi-dimensional arrays. It is also very efficient in handling a huge number of data elements. NumPy arrays use less memory than List data structures. Both the NumPy array and the list can be identified by their index value.

The NumPy library provides two methods for converting lists to arrays in Python.

Using numpy.array()
Using numpy.asarray()

Method 1: Using numpy.array()

In Python, the simplest way to convert a list to a NumPy array is with numpy.array() function. It takes an argument and returns a NumPy array. It creates a new copy in memory.

Program 1

# importing library of the array in python
import numpy
# initilizing elements of the list
a = [1, 2, 3, 4, 5, 6, 7, 8, 9]
# converting elements of the list into array elements
arr = numpy.array(a)
# displaying elements of the list
print ("List: ", a)
# displaying elements of the array
print ("Array: ", arr)

Output:

List:  [1, 2, 3, 4, 5, 6, 7, 8, 9]
Array:  [1 2 3 4 5 6 7 8 9]

Method 2: Using numpy.asarray()

In Python, the second method is numpy.asarray() function that converts a list to a NumPy array. It takes an argument and converts it to the NumPy array. It does not create a new copy in memory. In this, all changes made to the original array are reflected on the NumPy array.

Program 2

# importing library of the array in python
import numpy
# initilizing elements of the list
a = [1, 2, 3, 4, 5, 6, 7, 8, 9]
# converting elements of the list into array elements
arr = numpy.asarray(a)
# displaying elements of the list
print ("List:", a)
# displaying elements of the array
print ("Array: ", arr)

Output:

List:  [1, 2, 3, 4, 5, 6, 7, 8, 9]
Array:  [1 2 3 4 5 6 7 8 9]

Program 3

# importing library of the NumPy array in python
import numpy
# initilizing elements of the list
lst = [1, 2, 3, 4, 5, 6, 7, 8, 9]
# converting elements of the list into array elements
arr = numpy.asarray(lst)
# displaying elements of the list
print ("List:", lst)
# displaying elements of the array
print ("arr: ", arr)
# made another array out of arr using asarray function
arr1 = numpy.asarray(arr)
#displaying elements of the arr1 before the changes made
print("arr1: " , arr1)
#change made in arr1
arr1[3] = 23
#displaying arr1 , arr , list after the change has been made
print("lst: " , lst)
print("arr: " , arr)
print("arr1: " , arr1)

Output:

List: [1, 2, 3, 4, 5, 6, 7, 8, 9]
arr:  [1 2 3 4 5 6 7 8 9]
arr1:  [1 2 3 4 5 6 7 8 9]
lst:  [1, 2, 3, 4, 5, 6, 7, 8, 9]
arr:  [ 1  2  3 23  5  6  7  8  9]
arr1:  [ 1  2  3 23  5  6  7  8  9]