Python random.shuffle() function to shuffle list

In this article, we will learn how to shuffle the Python list randomly using random.shuffle() function of a random module. Also, learn how to shuffle string or any sequence in Python randomly. When we say shuffle a list, it means we are rearranging the order of items in a list randomly.

Goals of this lesson In this lesson, you’ll learn how to:

• Shuffle a list and string
• Shuffle list not in place.
• Shuffle two Python list at once with the same order
• Shuffle list in such a way that we will get the same result every time
• Shuffling multidimensional array in Python

The Syntax of random.shuffle

random.shuffle(x, random)

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

Parameters:

• x is any sequence you want to shuffle. x can be the list, string or tuple.
• The optional argument random is a function returning a random float number between 0.1 to 1.0. If not specified by default, Python uses random.random() function.

If you want to perform shuffling as per your need, then you can pass a custom random function in the place of a random argument, which will dictate shuffle function on how to randomizes the items of a list.

Return Value

The random.shuffle() shuffles 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 using random.shuffle()

The random.shuffle() is used to shuffle the list in place. i.e., it randomizes the order of items in a list, we call it a randomizes the elements of a list in place. for example, shuffling a list of cards. Now, Let’s see the example.

import random

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

random.shuffle(number_list)
print("List after first shuffle:", number_list)

random.shuffle(number_list)
print("List after second shuffle:", number_list)

Output:

Original list: [7, 14, 21, 28, 35, 42, 49, 56, 63, 70]
List after first shuffle: [35, 42, 63, 21, 7, 14, 70, 28, 49, 56]
List after second shuffle: [56, 35, 7, 70, 28, 42, 14, 63, 49, 21]

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

Randomly shuffle not in place

The random.shuffle() works in place and returns None, i.e., it changes the order of items in a list randomly. But most of the time, we need an original list. Is there a way of getting the original list after you shuffled?

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

• Make a copy of the original list into the new list before shuffling (Ideal and preferred)
• Shuffle list not in place to get the shuffled list in return instead of changing the original list

Option 1: Make a copy of the original list

import random

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

print("Original list : ", numbers)
print("List after shuffle", new_list)

Output:

Original list :  [33, 66, 99, 188, 256, 412, 748]
List after shuffle [412, 33, 256, 748, 99, 66, 188]

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

To perform shuffle not in-place we need to use a random.sample() function. The random.sample() function returns the random list with the number of the sample size you passed to it. For example, random.sample(myList, 3) will give us a list of 3 random items from a myList.

If we pass the sample size the same as the size of a list, it will return us the new randomly shuffle list of an original list. Let’s see the example. In this example, I am shuffling the list of Employee objects.

import random

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

emp1 = Employee("Ault", 10000)
emp2 = Employee("Abigail", 8000)
emp3 = Employee("Sampson", 12000)
emp4 = Employee("Joe", 7000)
empList = [emp1, emp2, emp3, emp4]

shuffledList = random.sample(empList, len(empList))
print("Printing new shuffled list of employee object")
for emp in shuffledList:
    print(emp.name, emp.salary)

Output:

Printing new shuffled list of employee object
Joe 7000
Ault 10000
Sampson 12000
Abigail 8000

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 random.seed() and random.shuffle() together we can generate the same shuffled list every time.

import random

numbers = [10, 20, 30, 40, 50, 60]
print ("Original list: ", numbers )
random.seed(4)
random.shuffle(numbers)
print("reshuffled list ", numbers)

random.seed(4)
random.shuffle(numbers)
print("reshuffled list ", numbers)

Output:

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

Shuffle two lists at once with the same order

Let’s assume if you want to Shuffle two list but also wants to 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

list1_names = ['Jon', 'Emma', 'Kelly', 'Jason']
list2_salary = [7000, 6500, 9000, 10000]

print("Lists before Shuffling")
print("Employee Names: ", list1_names)
print("Employee Salaries: ", list2_salary)

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

print("Lists after Shuffling")
print("Employee Names: ", list1_names)
print("Employee Salary: ", list2_salary)

print("Employee name and salary present index 3")
print(list1_names[3], list2_salary[3])

Output:

Lists before Shuffling
Employee Names:  ['Jon', 'Emma', 'Kelly', 'Jason']
Employee Salaries:  [7000, 6500, 9000, 10000]

Lists after Shuffling
Employee Names:  ('Jason', 'Jon', 'Kelly', 'Emma')
Employee Salary:  (10000, 7000, 9000, 6500)

Employee name and salary present index 3
Emma 6500

import random

# Shuffle a range of numbers
numbers = list(range(10))
random.shuffle(numbers)
print(numbers)

Shuffling a String

In this section, we will see how to shuffle string in Python. But it is not as simple as shuffling a list. If we try to rearrange a string’s characters using random.shuffle() you will get an error.

The reason behind this is a string is immutable. And You can’t modify the immutable objects in Python. The random.shuffle() function adjusts the position of the items. It changes the original object. 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)

You will get the 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.

Approach One

• Convert String to list
• Shuffle the list randomly
• Convert the shuffled list into String

import random

sampleStr = "PYnative"
print("Original String: ", sampleStr)
# convert string into list
char_list = list(sampleStr)
# shuffle list
random.shuffle(char_list)
# convert list to string
finalStr = ''.join(char_list)
print("shuffled String is: ", finalStr)

Output:

Original String:  pynative
shuffled String is:  anvtipye

Note: The above example shuffles the list in place. Let’s see how to get shuffled a list of the original list without changing it.

Approach Two: Shuffling a String, not in place

Using this approach, we can have the original string unchanged and get the new shuffled string in return. Also, we don’t need to convert string to list to get the shuffled string. i.e., To shuffle an immutable object like string and return a new shuffled string, we need to use random.sample(sampleStr, k=len(sampleStr)) instead.

import random

sampleStr = "PYnative"
print("Original String: ", sampleStr)
# shuffle string using random.sample()
finalStr = ''.join(random.sample(sampleStr, len(sampleStr)))
print("shuffled String is: ", finalStr)

Output:

Original String:  PYnative
shuffled String is:  vnYPatie

Shuffling multidimensional array

Let’s assume if you have a multidimensional array and want to shuffle it. Python’s NumPy module has a numpy.random package to generate random data. In this example, I am using Python’s Numpy module to create a 2-d array. Also, Using numpy.random.shuffle() function we can shuffle the multidimensional array. Now, Let’s see how to shuffle a multidimensional array in Python.

import numpy

print("Before Shufflling 2-dimensional array in Python")
sampleArray = numpy.arange(100, 240, 10)
sampleArray = sampleArray.reshape(7,2)
print (sampleArray)

print("After Shufflling 2-dimensional array in Python")
newArray = numpy.random.shuffle(sampleArray)
print (sampleArray)

Output:

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

Shuffle a dictionary in Python

Shuffling a dictionary is not possible in Python. However, we can rearrange the iteration order of keys of a dictionary.  Fetch all keys from a dictionary and add it in a list, shuffle that list and access dictionary values using newly shuffled keys.

import random

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

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

Using random.shuffle() on a generator

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

So What Do You Think?

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 Free Python Exercises and Quizzes to have a better understanding of working with random data in Python.