How to Choose Elements from the List with Different Probability using NumPy

In NumPy, numpy.random.choice() function allows us to randomly pick elements from a list. Unlike normal random selection, this method lets us assign different probabilities to each element, so some items are more likely to be chosen than others.

Here we select one element uniformly at random (equal probability for each item).

import numpy as np
arr = [1, 2, 3, 4]
num = np.random.choice(arr)
print(num)

4

Explanation: Since no probabilities are specified, each element in the list has the same chance of being selected.

Syntax

numpy.random.choice(a, size=None, replace=True, p=None)

Parameters:

• a: 1D array-like -> Input list or array to sample from.
• size: int or tuple, optional -> Number of samples to draw.
• replace: bool, optional -> If True (default), same element can be selected multiple times. If False, elements are chosen without replacement.
• p: 1D array-like, optional -> Probabilities associated with each element. Must sum to 1.

Return Value: Returns a NumPy array containing the randomly chosen elements.

Examples

Example 1: In this example, we randomly select one element from the list with equal probability.

import numpy as np
lst = [10, 20, 30, 40, 50]
num = np.random.choice(lst)
print("Selected:", num)

Selected: 20

Explanation: Here, every element has the same chance of being selected since no probability distribution is provided.

Example 2: In this example, we select the element 40 every time by assigning 100% probability to it.

import numpy as np
lst = [10, 20, 30, 40, 50]
res = np.random.choice(lst, 3, p=[0, 0, 0, 1, 0])
print("Selected list:", res)

Selected list: [40 40 40]

Explanation: The probability is set to 1 for element 40 and 0 for all others, so only 40 is selected repeatedly.

Example 3: Here we select elements 30 and 40 randomly with equal probability using the p parameter.

import numpy as np
lst = [10, 20, 30, 40, 50]
res = np.random.choice(lst, 3, p=[0, 0, 0.5, 0.5, 0])
print("Selected list:", res)

Selected list: [30 30 40]

Explanation: Only 30 and 40 are possible outcomes. Since both have equal probability (0.5 each), they appear randomly in the output.