How to Create Random Arrays with NumPy in Python

Use numpy.random.rand() to create an array of random floats between 0 and 1, or numpy.random.randint() for random integers within a range. Specify the shape as arguments to get arrays of any size.

Syntax

NumPy provides several functions to create random arrays:

• numpy.random.rand(d0, d1, ..., dn): Creates an array of given shape with random floats in [0, 1).
• numpy.random.randint(low, high=None, size=None): Creates an array of random integers from low (inclusive) to high (exclusive).

Here, d0, d1, ..., dn define the shape of the array, and size is the shape tuple for the output array.

python

import numpy as np

# Random floats array of shape (3, 2)
np.random.rand(3, 2)

# Random integers array of shape (4,) from 0 to 9
np.random.randint(0, 10, size=4)

Example

This example shows how to create a 3x3 array of random floats and a 1D array of 5 random integers between 10 and 20.

python

import numpy as np

# 3x3 array of random floats between 0 and 1
random_floats = np.random.rand(3, 3)

# 1D array of 5 random integers between 10 (inclusive) and 20 (exclusive)
random_ints = np.random.randint(10, 20, size=5)

print("Random floats array:\n", random_floats)
print("Random integers array:\n", random_ints)

Output

Random floats array:
 [[0.5488135  0.71518937 0.60276338]
 [0.54488318 0.4236548  0.64589411]
 [0.43758721 0.891773   0.96366276]]
Random integers array:
 [13 19 10 14 17]

Common Pitfalls

Common mistakes when creating random arrays include:

• Using randint without specifying high when you want a range (it defaults to None, which causes an error).
• Confusing the shape arguments for rand (positional shape) and randint (size keyword argument).
• Expecting rand to generate integers (it generates floats).

python

import numpy as np

# Wrong: missing 'high' argument causes error
# np.random.randint(5, size=3)  # This works, low=0, high=5

# Correct usage:
random_ints_correct = np.random.randint(0, 5, size=3)
print(random_ints_correct)

Output

[3 1 4]

Quick Reference

Function	Description	Example Usage
numpy.random.rand	Random floats in [0,1), shape as arguments	np.random.rand(2,3)
numpy.random.randint	Random integers in [low, high), size as shape	np.random.randint(0, 10, size=5)
numpy.random.randn	Random floats from standard normal distribution	np.random.randn(4)

Key Takeaways

Use np.random.rand() to create arrays of random floats between 0 and 1 with specified shape.

Use np.random.randint(low, high, size) to create arrays of random integers within a range.

Always specify the shape correctly: positional args for rand(), size= for randint().

rand() generates floats, randint() generates integers; don't confuse them.

Check arguments carefully to avoid errors like missing 'high' in randint().