Python random.shuffle() function to shuffle list

In this lesson, you will learn how to shuffle a Python list using the random.shuffle() function. Also, learn how to shuffle string, dictionary, or any sequence in Python.

When we say shuffle a list, it means a change in the order of list items. For example, shuffle a list of cards.

You’ll learn the following functions of a random module to randomize a list in Python.

Function	Description
random.shuffle(list1)	Shuffle list in-place (preferred way)
random.sample(seq, len(seq))	Shuffle list not in place to return a new shuffled list. (non-preferred way) OR To shuffle an immutable sequence such as string or range.
np.random.shuffle(array)	Shuffling multidimensional array

The random.shuffle() function

Syntax

random.shuffle(x, random)

It means shuffle a sequence x using a random function.

Parameters:

The random.shuffle() function takes two parameters. Out of the two, random is an optional parameter.

• x: It is a sequence you want to shuffle such as list.
• random: The optional argument random is a function returning a random float number between 0.1 to 1.0. This function decides how to shuffle a sequence. If not specified, by default Python uses the random.random() function.
  Note: this parameter deprecated since version 3.9, will be removed in version 3.11

Return Value

It shuffles sequence in place and doesn’t return anything, i.e., It returns None. This function changes the position of items in a mutable sequence.

Shuffle a List

Example: –

import random

number_list = [7, 14, 21, 28, 35, 42, 49, 56, 63, 70]
# Original list
print(number_list)
# Output [7, 14, 21, 28, 35, 42, 49, 56, 63, 70]

# List after first shuffle
random.shuffle(number_list)
print(number_list)
# Output [42, 28, 14, 21, 7, 35, 49, 63, 56, 70]

# List after second shuffle
random.shuffle(number_list)
print(number_list)
# Output [14, 21, 70, 28, 49, 35, 56, 7, 42, 63]

Note: As you can see in the output, the positions of list items are changed.

Try to solve: – Python random data generation Exercise

Randomly Shuffle Not in Place

As you know, the shuffle() works in place and returns None, i.e., it changes the order of items in the original list randomly. But most of the time, we need the original list or sequence.

We can keep the original list intact using the following two ways. These options don’t modify the original list but return a new shuffled list.

Option 1: Make a Copy of the Original List

Make a copy of the original list before shuffling (Ideal and preferred)

import random

numbers = [33, 66, 99, 188, 256, 412, 748]
# copy to new list
new_list = numbers.copy()
# shuffle the new list
random.shuffle(new_list)

print("Original list : ", numbers)
#  [33, 66, 99, 188, 256, 412, 748]

print("List after shuffle", new_list)
# Output [188, 412, 33, 256, 66, 748, 99]

Option 2: Shuffle list not in Place using random.sample()

Use the random.sample() function to shuffle list not in place to get the new shuffled list in return instead of changing the original list

The sample() function returns the random list with the sample size you passed to it. For example, sample(myList, 3) will return a list of 3 random items from a list.

If we pass the sample size the same as the original list’s size, it will return us the new shuffled list.

Let’s see the example. In this example, I am shuffling the list of Employee objects.

import random

# custom class
class Employee:
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary


emp1 = Employee("Kelly", 10000)
emp2 = Employee("Abigail", 8000)
emp3 = Employee("Sampson", 12000)
emp4 = Employee("Joe", 7000)
# list with 4 objects
emp_list = [emp1, emp2, emp3, emp4]

# print original list
for emp in emp_list:
    print(emp.name, emp.salary, end=', ')
# Output Kelly 10000, Abigail 8000, Sampson 12000, Joe 7000,

# shuffle list of objects
# sample size (k) = length of a list
shuffledList = random.sample(emp_list, k=len(emp_list))
print("\nPrinting new shuffled list of employee object")
for emp in shuffledList:
    print(emp.name, emp.salary, end=', ')
# Output Joe 7000, Kelly 10000, Abigail 8000, Sampson 12000,

Waring: As per the official Python documentation, for small len(x), the total number of permutations of x can quickly grow more extensive than the period of most random number generators. This implies that most permutations of a long sequence can never be generated. For example, a sequence of length 2080 is the largest that can fit within the Mersenne Twister random number generator period. So I advise you to use the use first approach.

Shuffle Two Lists At Once With Same Order

Let’s assume if you want to Shuffle two lists and maintain the same shuffle order. For example, One list contains employee names, and the other includes a salary. Let’s see how to randomize multiple lists by maintaining their order.

import random

# list of names
employees = ['Jon', 'Emma', 'Kelly', 'Jason']
# list of numbers
salary = [7000, 6500, 9000, 10000]

# Lists before Shuffling
print("Employee Names: ", employees)
# output ['Jon', 'Emma', 'Kelly', 'Jason']
print("Employee Salaries: ", salary)
# Output [7000, 6500, 9000, 10000]

# To Shuffle two List at once with the same order
mapIndexPosition = list(zip(employees, salary))
random.shuffle(mapIndexPosition)
# make list separate
list1_names, list2_salary = zip(*mapIndexPosition)

# Lists after Shuffling
print("Employee Names: ", list1_names)
# Output ('Emma', 'Jon', 'Kelly', 'Jason')
print("Employee Salary: ", list2_salary)
# output (6500, 7000, 9000, 10000)

# Employee name and salary present index 3
print(list1_names[3], list2_salary[3])
# Output Jason 10000

Shuffling NumPy Multidimensional Array

NumPy module has a numpy.random package to generate random data. In this example, I am using Python’s Numpy module to create a 2d array. Also, Using numpy.random.shuffle() function, we can shuffle the multidimensional array.

import numpy as np

print('Before shuffling 2dimensional array')
sample_array = np.arange(100, 240, 10)
sample_array = sample_array.reshape(7, 2)
print(sample_array)

print('After shuffling 2dimensional array')
np.random.shuffle(sample_array)
print(sample_array)

Output:

Before shuffling 2dimensional array
 [[100 110]
  [120 130]
  [140 150]
  [160 170]
  [180 190]
  [200 210]
  [220 230]]
 After shuffling 2dimensional array
 [[160 170]
  [140 150]
  [200 210]
  [220 230]
  [120 130]
  [100 110]
  [180 190]]

Shuffle a List to Get the Same Result Every time

Let’s how to seed the random generator in such a way that shuffling produces the same result every time. Using the seed() and shuffle() together, we can generate the same shuffled list every time.

Do you know how PRNG works in Python?

Python’s random module is not truly random. It is pseudo-random (PRNG), i.e., deterministic. The random module uses the seed value as a base to generate a random number. By default, current system time is used as a seed value. If we change the seed value, we can change the output.

import random

numbers = [10, 20, 30, 40, 50, 60]
print("Original list: ", numbers)

# shuffle 3 times
for i in range(3):
    # seed PRNG
    random.seed(4)
    # shuffle list
    random.shuffle(numbers)
    print("result list ", numbers)

Output:

Original list:  [10, 20, 30, 40, 50, 60]

result list  [40, 60, 50, 10, 30, 20]
result list  [10, 20, 30, 40, 50, 60]
result list  [40, 60, 50, 10, 30, 20]

Note: We are getting the same list because we use the same seed value before calling the shuffle function. This is just a simple example. To make it work with any list, we need to find the exact seed root number for that list, which will produce the output we desire.

Shuffle a String

In this section, we will see how to shuffle String in Python. But it is not as simple as shuffling a list. You will get an error if you try to shuffle a string using the shuffle() method.

Because a string is an immutable type, and You can’t modify the immutable objects in Python. The random.shuffle() doesn’t’ work with String. I.e., It can’t accept string argument. Let’s understand this with the help of the following example.

import random

string_one = "PYnative"
random.shuffle(string_one)
print(string_one)
# TypeError: 'str' object does not support item assignment.

We have a solution to this. We can shuffle a string using various approaches. Let see each one by one.

Shuffle a String by Converting it to a List

Convert String to list and Shuffle the list randomly, again convert the shuffled list into String

import random

sample_str = "PYnative"
# Original string
print(sample_str)
# 'PYnative'

# convert string into list
char_list = list(sample_str)
# shuffle list
random.shuffle(char_list)

# convert list to string
final_str = ''.join(char_list)

# shuffled list
print(final_str)
# Output 'tiaeYPvn'

Approach Two: Shuffling a String, not in place

Using this approach, we can keep the original string unchanged and get the new shuffled string in return. Also, we don’t need to convert the string to a list to get the shuffled string.

The sample() function returns a sample from a sequence as per the sample size you passed to it. For example, sample(str, 3) will return a list of 3 random characters from a list.

If we pass the sample size the same as the string size, it will return us the new shuffled string of characters.

import random

sample_str = "PYnative"
print(sample_str)
# 'PYnative'

# shuffle string using random.sample()
final_str = ''.join(random.sample(sample_str, len(sample_str)))
print(final_str)
# Output 'ePtaYivn'

Shuffle Range of Integers

A range() function returns a sequence of numbers.

The range() doesn’t return the list, so when you try to run shuffle(range(10)), you will get an error. To shuffle numbers in the range(10), first convert the range to a list.

import random

# Shuffle a range of numbers
numbers = list(range(10))
random.shuffle(numbers)
print(numbers)
# Output [1, 7, 0, 3, 2, 9, 6, 8, 4, 5]

Shuffle a Dictionary in Python

Shuffling a dictionary is not possible in Python. However, we can rearrange the order of keys of a dictionary.

• Fetch all keys from a dictionary as a list.
• Shuffle that list and access dictionary values using shuffled keys.

import random

student_dict = {'Eric': 80, 'Scott': 75, 'Jessa': 95, 'Mike': 66}
print("Dictionary Before Shuffling")
print(student_dict)
keys = list(student_dict.keys())
random.shuffle(keys)

ShuffledStudentDict = dict()
for key in keys:
    ShuffledStudentDict.update({key: student_dict[key]})

print("\nDictionary after Shuffling")
print(ShuffledStudentDict)

Output:

Dictionary before shuffling
{'Eric': 80, 'Scott': 75, 'Jessa': 95, 'Mike': 66}

Dictionary after shuffling
{'Jessa': 95, 'Eric': 80, 'Mike': 66, 'Scott': 75}

Shuffle a Python generator

The random.shuffle() needs to know the sequence’s size to shuffle the sequence uniformly. If you try to shuffle a generator object using it, you will get a TypeError: the object of type 'generator' has no len().

As the generator cannot provide us the size we need to convert it into a list to shuffle it.

import random

def sample_generator():
    yield 25
    yield 50
    yield 75
    yield 100

print("Generator")
for i in sample_generator():
    print(i, end=", ")

# Shuffle generator
newList = list(sample_generator())
random.shuffle(newList)
print("\nPrint shuffled generator")
for i in newList:
    print(i, end=", ")

Next Steps

I want to hear from you. What do you think of this article on random.shuffle()? Or maybe I missed one of the usages of random.shuffle(). Either way, let me know by leaving a comment below.

Also, try to solve the following exercise and quiz to have a better understanding of working with random data in Python.

• Python random data generation Exercise
• Python random data generation Quiz