Numpy random Examples | rand() | randint() function


Written by - Bashir Alam
Reviewed by - Deepak Prasad

Getting started with NumPy Random Module

NumPy, which stands for Numerical Python, is an essential library for anyone in the field of data science, machine learning, or scientific computing. One of its lesser-known but powerful sub-modules is numpy.random. The "NumPy Random" module provides a host of methods and functionalities to generate random numbers and perform various random operations. Whether you are building a machine learning model, simulating real-world scenarios, or just looking to understand your data better, NumPy Random has got you covered.

 

What is NumPy Random?

The NumPy Random module is essentially a suite of functions based on random number generation. From simulating data to initializing algorithms and conducting statistical tests, this module is incredibly versatile and useful. Unlike Python's native random library, NumPy Random is more efficient and better integrated with NumPy functionalities, allowing for seamless operations on NumPy arrays.

 

Installing NumPy

Installing NumPy is as simple as running a single command in your terminal. There are several ways to install it, but the most common methods are through package managers like pip or conda.

Using pip

pip install numpy

Using conda

conda install numpy

These commands will download and install the latest version of NumPy along with any dependencies that it needs. If you're running into issues or need to install a specific version, be sure to consult the official NumPy documentation .

 

Importing the Random Module

Once you've successfully installed NumPy, you can import its random module to start generating random numbers.

To import the random module, you can use the following code:

import numpy as np

Now, the random module can be accessed through np.random. For example, generating a random integer between 0 and 9 would be:

random_integer = np.random.randint(0, 10)
print("Random integer:", random_integer)

Alternatively, you can import specific functions from the random module, like so:

from numpy.random import randint, rand

Now you can use randint and rand directly:

random_integer = randint(0, 10)
random_float = rand()

 

Generating Random Floats

Floats are real numbers that have decimal points. NumPy offers two primary methods for generating random floats: random.rand() and random.random().

 

random.rand()

This function returns random floats in a half-open interval [0.0, 1.0). The numbers are sampled from a uniform distribution over that range. You can also create multi-dimensional arrays of random floats by providing dimensions as arguments.

Example:

import numpy as np

# Generate a single random float
single_float = np.random.rand()
print("Single random float:", single_float)

# Generate an array of random floats
array_float = np.random.rand(5)
print("Array of random floats:", array_float)

# Generate a 2D array of random floats
array_2D_float = np.random.rand(3, 3)
print("2D array of random floats:\n", array_2D_float)

 

random.random()

The random.random() function also returns a random float in the interval [0.0, 1.0). The key difference is that random.random() does not directly support generating arrays of random numbers. You need to use a loop or array broadcasting for that purpose.

# Generate a single random float
single_float = np.random.random()
print("Single random float:", single_float)

 

Generating Random Integers

When you need random integers, you can use the random.randint() function.

 

random.randint()

The random.randint() function returns random integers from the specified range. You can specify the range by providing the low and high values as arguments. Optionally, you can also specify the size parameter to generate an array of random integers.

Example:

# Generate a single random integer between 0 and 9
single_integer = np.random.randint(0, 10)
print("Single random integer:", single_integer)

# Generate an array of 5 random integers between 0 and 9
array_integer = np.random.randint(0, 10, size=5)
print("Array of random integers:", array_integer)

 

Understanding Distributions

In the field of statistics and data science, distributions are critical for understanding and interpreting data. The NumPy Random module allows you to generate random numbers from a variety of distributions. Below, we explore some of the most commonly used distributions and how to generate random numbers from them using NumPy.

 

Uniform Distribution - random.uniform()

In a uniform distribution, all numbers in a given range are equally likely to be chosen. The random.uniform() function returns a random float number between a specified low and high value.

Example:

import numpy as np

# Generate a single random float between 10 and 20
single_uniform = np.random.uniform(10, 20)
print("Single random float from uniform distribution:", single_uniform)

 

Normal Distribution - random.normal()

The normal distribution, also known as the Gaussian distribution, is a bell-shaped distribution where numbers close to the mean are more frequent. The random.normal() function returns a random float number sampled from a normal distribution with a specified mean (loc) and standard deviation (scale).

Example:

# Generate a single random float with mean 0 and standard deviation 1
single_normal = np.random.normal(0, 1)
print("Single random float from normal distribution:", single_normal)

 

Binomial Distribution - random.binomial()

In a binomial distribution, there are only two possible outcomes: success or failure. The random.binomial() function returns the number of successes in a given number of trials (n) with a specified probability of success (p).

Example:

# 10 trials with a 0.5 probability of success
single_binomial = np.random.binomial(10, 0.5)
print("Single random number from binomial distribution:", single_binomial)

 

Poisson Distribution - random.poisson()

The Poisson distribution models the number of events occurring within a fixed interval of time or space. The random.poisson() function returns a random number representing the number of events occurring within a given time interval, based on a specified average rate (lam).

Example:

# Average rate of 3 events per interval
single_poisson = np.random.poisson(3)
print("Single random number from Poisson distribution:", single_poisson)

 

Other Distributions

In addition to the distributions above, NumPy Random also supports several other distributions like exponential (random.exponential()), geometric (random.geometric()), and many more. Each of these functions offers a way to model different kinds of data and phenomena.

 

Random Sampling

Random sampling is an essential technique in statistics and data analysis. Whether you're building machine learning models, conducting scientific experiments, or performing data audits, being able to create random samples from a dataset is crucial. NumPy's random module provides useful functions for such operations, with random.choice() being particularly versatile.

 

Simple Random Sampling - random.choice()

Simple random sampling is the basic form of sampling where each item in the dataset has an equal chance of being selected. The random.choice() function allows you to generate a random sample from a given 1-D array. If you don't specify an array, it will default to generating a random integer.

Example:

import numpy as np

# Randomly pick one item from a list
single_sample = np.random.choice([1, 2, 3, 4, 5])
print("Single random sample:", single_sample)

 

Random Sample from a Given Array - random.choice(a, size, replace, p)

The power of random.choice() really comes into play when you wish to generate more complex random samples from a given array.

  • a: The array from which to generate samples.
  • size: The number of samples to generate. Can be an integer or tuple (for multi-dimensional arrays).
  • replace: Whether to sample with replacement (True) or without replacement (False).
  • p: The probabilities associated with each entry in the array.

Example:

# Randomly pick 3 items from a list with replacement
sample_with_replacement = np.random.choice([1, 2, 3, 4, 5], size=3, replace=True)
print("Sample with replacement:", sample_with_replacement)

# Randomly pick 3 items from a list without replacement
sample_without_replacement = np.random.choice([1, 2, 3, 4, 5], size=3, replace=False)
print("Sample without replacement:", sample_without_replacement)

# Randomly pick 3 items from a list with specified probabilities
sample_with_prob = np.random.choice([1, 2, 3, 4, 5], size=3, p=[0.1, 0.2, 0.3, 0.2, 0.2])
print("Sample with probabilities:", sample_with_prob)

 

Array Operations

Randomly manipulating arrays is a common operation in data science, machine learning, and scientific computing. Whether you are shuffling a dataset, generating test data, or initializing variables, NumPy's random module provides convenient and efficient methods to carry out these operations.

 

Shuffle an Array - random.shuffle()

Shuffling an array can be useful in numerous scenarios, such as when you're preparing a dataset for training/testing splits in machine learning. The random.shuffle() function shuffles an array along the first axis. It modifies the array in place and does not return a value. Note that the shuffle is not "stable," meaning that the order of equivalent elements may change.

Example:

import numpy as np

# Create an array
original_array = np.array([1, 2, 3, 4, 5])

# Shuffle the array
np.random.shuffle(original_array)

print("Shuffled array:", original_array)

 

Generate Random Arrays

Generating random arrays is essential for simulations, initializing algorithms, or creating synthetic data. Two commonly used functions for this are random.rand() and

 

random.rand()

The random.rand() function creates an array of specified shape and fills it with random floats in the interval [0, 1). The numbers are drawn from a uniform distribution.

Example:

# Generate a 2x2 array of random floats between 0 and 1
random_array = np.random.rand(2, 2)
print("Random array with uniform distribution:\n", random_array)

 

random.randn()

The random.randn() function returns an array of specified shape, filled with random floats sampled from a normal (Gaussian) distribution of mean 0 and variance 1.

Example:

# Generate a 2x2 array of random floats from a normal distribution
random_array_normal = np.random.randn(2, 2)
print("Random array with normal distribution:\n", random_array_normal)

 

Seed in Random Number Generation with NumPy

Random number generation seems entirely random, but in practice, these numbers are generated using algorithms that rely on initial input values, known as "seeds." Utilizing seeds ensures that you can replicate the same "random" results, offering both repeatability and predictability. This feature is particularly useful in debugging and comparison studies. Below, we explore what a seed is, and how to set it using NumPy's random module.

 

What is a Seed?

In the context of random number generation, a seed is an initial value used by an algorithm to generate a sequence of random numbers. If you start from the same seed, you get the very same sequence of random numbers. Therefore, setting the seed can be crucial for research, debugging, and sharing code with others to produce replicable results.

You can set the seed in NumPy using the random.seed() function. This function takes an integer as an argument, initializing the random number generator with that seed value.

 

Example 1: Replicating Results

Here's how you can set a seed and generate random numbers to produce replicable results.

import numpy as np

# Set the seed
np.random.seed(42)

# Generate random integer
random_integer = np.random.randint(0, 10)
print("Random integer:", random_integer)  # Output will always be 6 with this seed

# Generate random array
random_array = np.random.rand(3)
print("Random array:", random_array)  # Output will be same when seed is 42

 

Example 2: Comparison Without and With Seed

To demonstrate the importance of the seed, let's generate random numbers without setting the seed and then with setting the seed.

# Without seed
random_integer1 = np.random.randint(0, 10)
random_integer2 = np.random.randint(0, 10)
print("Random integers without seed:", random_integer1, random_integer2)  # Outputs will vary each run

# With seed
np.random.seed(42)
random_integer1 = np.random.randint(0, 10)
np.random.seed(42)
random_integer2 = np.random.randint(0, 10)
print("Random integers with seed:", random_integer1, random_integer2)  # Outputs will be same each run (both 6)

 

Performance Considerations: Python's Native random vs. NumPy's random

When dealing with a large amount of data or running intensive simulations, the performance of the random number generation can be a concern. Both Python's native random library and NumPy's random module offer ways to generate random numbers, but they perform differently in terms of speed. Below, we compare their performance using examples and output data.

We'll use Python's timeit module to compare the time taken by each method for generating random numbers.

Example: Generate 10,000 Random Floats

import random
import numpy as np
import timeit

# Python's native random
def generate_native_random():
    return [random.random() for _ in range(10000)]

# NumPy's random
def generate_numpy_random():
    return np.random.rand(10000)

# Time taken for Python's native random
time_native = timeit.timeit(generate_native_random, number=100)
print(f"Time taken using Python's native random: {time_native:.6f} seconds")

# Time taken for NumPy's random
time_numpy = timeit.timeit(generate_numpy_random, number=100)
print(f"Time taken using NumPy's random: {time_numpy:.6f} seconds")

Here, the output data would depend on the specific hardware and software configuration of your machine. However, you'll generally notice that NumPy's random number generation is faster. An example output could look like:

Time taken using Python's native random: 0.768987 seconds
Time taken using NumPy's random: 0.034560 seconds

As evident from the example output data, NumPy's random is significantly faster than Python's native random for generating 10,000 random floats. This speed advantage comes from the underlying implementation of NumPy, which is written in C and optimized for performance. The array-based operations are particularly efficient when you need to generate large arrays of random numbers.

 

Further Reading

random numbers in numpy
Numpy and random numbers
rand method in numpy

 

Bashir Alam

He is a Computer Science graduate from the University of Central Asia, currently employed as a full-time Machine Learning Engineer at uExel. His expertise lies in OCR, text extraction, data preprocessing, and predictive models. You can reach out to him on his Linkedin or check his projects on GitHub page.

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