NumPy array_split(): Split Arrays into Multiple Sub-Arrays

When the number of sections does not evenly divide the axis length, array_split() automatically adjusts sub-array sizes so that earlier sections contain one more element than later sections. For strict equal divisions, see split(). For stacking operations, see append().

Syntax and Parameters 🔝

numpy.array_split(ary, indices_or_sections, axis=0)

Equal Sections Splitting 🔝

When the number of sections evenly divides the array length, array_split() produces sub-arrays of equal size:

import numpy as np

my_ar = np.arange(9)
splits = np.array_split(my_ar, 3)
print(splits)

assert len(splits) == 3
assert np.array_equal(splits[0], np.array([0, 1, 2]))

Expected output

[array([0, 1, 2]), array([3, 4, 5]), array([6, 7, 8])]

Unequal Sections Splitting 🔝

When N does not divide evenly into the requested number of sections, array_split() distributes the remainder across the initial sections:

my_ar = np.arange(9)
print(np.array_split(my_ar, 5))

print(np.array_split(my_ar, 4))

Expected output

[array([0, 1]), array([2, 3]), array([4, 5]), array([6, 7]), array([8])]
[array([0, 1, 2]), array([3, 4]), array([5, 6]), array([7, 8])]

Splitting 2D Arrays 🔝

By default, splitting operates along axis=0 (splitting rows):

my_data = np.array([[6, 3, 2], [7, 2, 2], [6, 2, 9]])
print(np.array_split(my_data, 3))

Expected output

[array([[6, 3, 2]]), array([[7, 2, 2]]), array([[6, 2, 9]])]

Accessing Sub-Array Elements 🔝

Because array_split() returns a list of sub-arrays, individual items can be accessed using standard indexing:

my_data = np.array([[6, 3, 2], [7, 2, 2], [6, 2, 9]])
my_ar = np.array_split(my_data, 3)

print(my_ar[1])       # [[7 2 2]]
print(my_ar[1][0])    # [7 2 2]
print(my_ar[1][0][2]) # 2

assert my_ar[1][0][2] == 2

Expected output

[[7 2 2]]
[7 2 2]
2

Float Dtype Splitting 🔝

Splitting floating-point arrays preserves precision across chunks:

my_ar = np.arange(9.)
print(np.array_split(my_ar, 4))

Expected output

[array([0., 1., 2.]), array([3., 4.]), array([5., 6.]), array([7., 8.])]

Practice in Google Colab 🔝

Test array_split() on 1D and 2D arrays, explore unequal section distribution, and run verification test suites in our interactive Google Colab companion notebook:

Interactive Practice: Colab & GitHub

Launch the notebook directly in Google Colab to run live code cells or inspect the source repository on GitHub:

View on GitHub

Continue exploring related array manipulation functions: array(), zeros(), append(), insert(), and reshape().

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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