Randomly select elements from list without repetition in Python

We are given a list, and our task is to randomly select elements from it without repetition. This means that once an element is selected, it should not be picked again. For example, given a = [10, 20, 30, 40, 50], selecting three elements randomly could result in [30, 10, 50], but the same element should not appear twice. Let's discuss different ways to do this in Python.

Using random.sample()

random.sample() function selects unique elements from a list in a single step without repetition.

import random  
 
a = [10, 20, 30, 40, 50]  

# Selecting 3 unique elements  
res = random.sample(a, 3)  

print(res)  

[50, 30, 10]

Explanation:

• random.sample(a, 3) selects 3 unique elements from a.
• The function ensures no duplicates and maintains the order of selection.
• This method is efficient because it handles selection in a single operation.

Let's explore some more ways and see how we can randonly select elements from list without repetition in python.

Using random.shuffle() and Slicing

random.shuffle() function randomly rearranges the list, and we can take the first n elements as the selection.

import random  

a = [10, 20, 30, 40, 50]  

# Shuffling the list  
random.shuffle(a)  

# Selecting first 3 elements  
res = a[:3]  

print(res)

[20, 40, 30]

Explanation:

• random.shuffle(a) rearranges elements in place.
• Slicing a[:3] takes the first 3 elements from the shuffled list.
• This method is useful when order randomness matters.

Using random.choice()

random.choice() function picks a random element, and we can remove selected elements to avoid repetition.

import random  

a = [10, 20, 30, 40, 50]  

# Selecting 3 unique elements  
res = []  
for _ in range(3):  
    choice = random.choice(a)  # Pick a random element  
    res.append(choice)  
    a.remove(choice)  # Remove chosen element to prevent repetition  

print(res) 

[20, 10, 30]

Explanation:

• random.choice(a) selects a random element.
• a.remove(choice) removes the selected element to avoid repetition.
• This method modifies the original list and is less efficient for large lists.

Using set()

We can use a set to keep track of selected elements and avoid modifying the original list.

import random  
 
a = [10, 20, 30, 40, 50]  

# Selecting 3 unique elements  
selected = set()  
while len(selected) < 3:  
    selected.add(random.choice(a))  

res = list(selected)  

print(res)

[40, 10, 20]

Explanation:

• random.choice(a) picks a random element.
• selected.add(choice) ensures no duplicates.
• The loop continues until 3 unique elements are selected.