Python | Generate random number except K in list

Sometimes, while working with python, we can have a problem in which we need to generate random number. This seems quite easy but sometimes we require a slight variation of it. That is, we require to generate random number from a list except K. Lets discuss certain ways in which this task can be performed. 

Method #1 : Using choice() + list comprehension The combination of above functions can be used to perform this task. In this, we first filter out the numbers except K using list comprehension and then feed that list to choice() for random number generation. 

Python3

# Python3 code to demonstrate
# Generate random number except K in list
# using choice() + list comprehension
import random

# Initializing list
test_list = [4, 7, 8, 4, 6, 10]

# printing original list
print("The original list is : " + str(test_list))

# Initializing K
K = 4

# Generate random number except K in list
# using choice() + list comprehension
res = random.choice([ele for ele in test_list if ele != K])

# printing result
print ("The random number except K is : " + str(res))

Output : 

The original list is : [4, 7, 8, 4, 6, 10]
The random number except K is : 8

Method #2 : Using filter() + lambda + choice() This is yet another way in which this task can be performed. In this, we perform method of creating new list using filter and lambda. 

Python3

# Python3 code to demonstrate
# Generate random number except K in list
# using choice() + filter() + lambda
import random

# Initializing list
test_list = [4, 7, 8, 4, 6, 10]

# printing original list
print("The original list is : " + str(test_list))

# Initializing K
K = 4

# Generate random number except K in list
# using choice() + filter() + lambda
res = random.choice(list(filter(lambda ele: ele != K, test_list)))

# printing result
print ("The random number except K is : " + str(res))

Output : 

The original list is : [4, 7, 8, 4, 6, 10]
The random number except K is : 8

Method 3: Using random.sample()
This method uses the random.sample() function from the random module to select a random element from the list without replacement, which means that the selected element will not be present in the list after being selected.

Python3

#Python3 code to demonstrate
#Generate random number except K in list
#using random.sample()
import random

#Initializing list
test_list = [4, 7, 8, 4, 6, 10]

#printing original list
print("The original list is : " + str(test_list))

#Initializing K
K = 4

#Generate random number except K in list
#using random.sample()
res = random.sample([ele for ele in test_list if ele != K], 1)[0]

#printing result
print ("The random number except K is : " + str(res))

Output

The original list is : [4, 7, 8, 4, 6, 10]
The random number except K is : 7

Time complexity: O(n) where n is the length of the list
Auxiliary Space: O(n)

Explanation:
The code filters out all elements equal to K using a list comprehension and then selects one random element from the filtered list using random.sample(). The selected element is then accessed using [0] indexing.