NumPy ndarray.tolist() Method

NumPy ndarray.tolist()

The numpy.ndarray.tolist() method converts a NumPy array into a nested list. This method returns a standard Python list representation of the array, making it useful for interoperability with Python data structures.

Syntax

ndarray.tolist()

Return Value

Returns a nested Python list representation of the array. The structure of the list matches the shape of the original array.

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Examples

1. Converting a 1D NumPy Array to a List

In this example, we create a 1D NumPy array and convert it into a Python list using tolist().

import numpy as np

# Creating a 1D NumPy array
arr = np.array([1, 2, 3, 4, 5])

# Converting the NumPy array to a Python list
list_result = arr.tolist()

# Printing the result
print(list_result)

Output:

[1, 2, 3, 4, 5]

2. Converting a 2D NumPy Array to a Nested List

Here, we convert a 2D NumPy array into a nested Python list.

import numpy as np

# Creating a 2D NumPy array
arr = np.array([[1, 2, 3], 
                [4, 5, 6]])

# Converting the NumPy array to a Python nested list
list_result = arr.tolist()

# Printing the result
print(list_result)

Output:

[[1, 2, 3], [4, 5, 6]]

3. Converting a 3D NumPy Array to a Nested List

This example demonstrates converting a 3D NumPy array into a deeply nested Python list.

import numpy as np

# Creating a 3D NumPy array
arr = np.array([[[1, 2], [3, 4]],
                [[5, 6], [7, 8]]])

# Converting the NumPy array to a nested Python list
list_result = arr.tolist()

# Printing the result
print(list_result)

Output:

[[[1, 2], [3, 4]], [[5, 6], [7, 8]]]

4. Converting a NumPy Array with Floating Point Numbers to a List

In this example, we convert an array containing floating-point numbers into a Python list.

import numpy as np

# Creating a NumPy array with floating-point numbers
arr = np.array([1.5, 2.3, 3.8, 4.1])

# Converting the NumPy array to a Python list
list_result = arr.tolist()

# Printing the result
print(list_result)

Output:

[1.5, 2.3, 3.8, 4.1]

5. Converting a NumPy Array with Mixed Data Types to a List

Here, we convert an array with mixed data types (integers and strings) into a Python list.

import numpy as np

# Creating a NumPy array with mixed data types
arr = np.array([1, "Hello", 3.5])

# Converting the NumPy array to a Python list
list_result = arr.tolist()

# Printing the result
print(list_result)

Output:

[1, 'Hello', 3.5]

Since NumPy arrays with mixed data types automatically convert elements to a common type (string in this case), the resulting list retains the same mixed structure.