Python program to select Random value from list of lists (original) (raw)

Last Updated : 08 May, 2023

Given a list of lists. The task is to extract a random element from it.

Examples:

Input : test_list = [[4, 5, 5], [2, 7, 4], [8, 6, 3]] Output : 7 Explanation : Random number extracted from Matrix.

Input : test_list = [[4, 5, 5], [2, 7, 4], [8, 6, 3]], r_no = 2 Output : 6 Explanation : Random number extracted from 2nd row from Matrix.

Method #1: Using chain.from_iterable() + random.choice()

In this, we flatten the Matrix to list using from_iterable() and choice() is used to get a random number from the list.

Python3 `

Python3 code to demonstrate working of

Random Matrix Element

Using chain.from_iterables() + random.choice()

from itertools import chain import random

Initializing list

test_list = [[4, 5, 5], [2, 7, 4], [8, 6, 3]]

Printing original list

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

choice() for random number, from_iterables for flattening

res = random.choice(list(chain.from_iterable(test_list)))

Printing result

print("Random number from Matrix : " + str(res))

`

Output

The original list is : [[4, 5, 5], [2, 7, 4], [8, 6, 3]] Random number from Matrix : 6

Method #2 : Using choice() to get element from particular row

If a row is mentioned, the choice() method can be used to get a random element from that row.

Python3 `

Python3 code to demonstrate working of

Random Matrix Element

Using random.choice() [if row number given]

import random

initializing list

test_list = [[4, 5, 5], [2, 7, 4], [8, 6, 3]]

printing original list

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

initializing Row number

r_no = [0, 1, 2]

choice() for random number, from_iterables for flattening

res = random.choice(test_list[random.choice(r_no)])

printing result

print("Random number from Matrix Row : " + str(res))

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Output

The original list is : [[4, 5, 5], [2, 7, 4], [8, 6, 3]] Random number from Matrix Row : 7

Method 3: Using the numpy package.

Approach:

1. Import the numpy package.
2. Initialize the 2D matrix using the numpy array() method.
3. Use the numpy random.choice() method to generate a random number from the matrix.
4. Print the result. Python3 `

import numpy as np import random

initializing list

test_list = [[4, 5, 5], [2, 7, 4], [8, 6, 3]]

printing original list

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

initializing Row number

r_no = [0, 1, 2]

Converting list to numpy array

arr = np.array(test_list)

Generating random number from matrix

using numpy random.choice() method

res = np.random.choice(arr[random.choice(r_no)])

Printing result

print("Random number from Matrix Row : " + str(res))

`

Output

The original list is : [[4, 5, 5], [2, 7, 4], [8, 6, 3]] Random number from Matrix Row : 7

Time Complexity: O(1)
Auxiliary Space: O(1)

Method 3 : Using list comprehension and random.sample()

Approach:

1. Import the random module
2. Initialize the list and print the original list
3. Generate a random number for the row index using random.randint() method
4. Use list comprehension to extract the row corresponding to the random index generated in step 3
5. Use the random.sample() method to get a sample of elements from the row, with a sample size of 1.
6. Get the randomly selected element from the sample and store it in a variable.
7. Print the randomly selected element from the matrix row. Python3 `

import random

initializing list

test_list = [[4, 5, 5], [2, 7, 4], [8, 6, 3]]

printing original list

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

generating random row index

row_index = random.randint(0, len(test_list)-1)

extracting the row corresponding to the random index using list comprehension

row = [test_list[row_index][i] for i in range(len(test_list[row_index]))]

getting a sample of elements from the row using random.sample()

sample = random.sample(row, k=1)

getting the randomly selected element from the sample

res = sample[0]

printing result

print("Random number from Matrix Row : " + str(res))

`

Output

The original list is : [[4, 5, 5], [2, 7, 4], [8, 6, 3]] Random number from Matrix Row : 7

Time Complexity: O(n) - linear time complexity as we are traversing the matrix once using list comprehension to extract the row.
Auxiliary Space: O(n) - linear auxiliary space as we are creating a new list to store the extracted row.