How to Create a 2D Array in NumPy: Simple Guide

To create a 2D array in NumPy, use the numpy.array() function with a list of lists as input. Each inner list represents a row, forming a matrix-like structure.

Syntax

The basic syntax to create a 2D array in NumPy is:

• numpy.array(object): Converts the input object (usually a list of lists) into a NumPy array.
• Each inner list represents a row in the 2D array.

python

import numpy as np

array_2d = np.array([[1, 2, 3], [4, 5, 6]])

Example

This example shows how to create a 2D array with two rows and three columns, then print it.

python

import numpy as np

array_2d = np.array([[10, 20, 30], [40, 50, 60]])
print(array_2d)

Output

[[10 20 30]
 [40 50 60]]

Common Pitfalls

Common mistakes when creating 2D arrays include:

• Using uneven inner lists, which creates an array of lists instead of a 2D numeric array.
• Forgetting to import NumPy before using np.array().
• Passing a flat list instead of a list of lists, which creates a 1D array.

python

import numpy as np

# Wrong: uneven inner lists
array_wrong = np.array([[1, 2], [3, 4, 5]])
print(array_wrong)

# Right: even inner lists
array_right = np.array([[1, 2, 0], [3, 4, 5]])
print(array_right)

Output

[list([1, 2]) list([3, 4, 5])]
[[1 2 0]
 [3 4 5]]

Quick Reference

Tips for creating 2D arrays in NumPy:

• Use np.array() with a list of lists.
• Ensure all inner lists have the same length.
• Check the shape with .shape attribute.
• Use dtype parameter to specify data type if needed.

Key Takeaways

Use np.array() with a list of lists to create a 2D array.

All inner lists must have the same length for a proper 2D array.

Check the array shape with the .shape attribute.

Avoid uneven inner lists to prevent creating arrays of lists.

Always import NumPy before creating arrays.