NumPy Array Splitting: A Complete Guide

In data analysis and manipulation, the ability to split arrays into smaller arrays is as essential as combining them. NumPy provides several functions to split arrays, such as np.split , np.hsplit , and np.vsplit . Understanding how to utilize these functions allows for more efficient and flexible data manipulation. This blog post will cover the methods you can use to split NumPy arrays and provide examples for each.

Introduction to Array Splitting in NumPy

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Splitting arrays can be useful in situations where data sets need to be divided into smaller chunks for cross-validation in machine learning, for distributed processing, or simply for organizing data more effectively.

The Split Function: np.split

The primary function for splitting arrays in NumPy is np.split . It divides an array into multiple sub-arrays of equal or near-equal size.

Syntax and Parameters

numpy.split(ary, indices_or_sections, axis=0) 
  • ary : The array to be divided.
  • indices_or_sections : Can be an integer, indicating the number of equal-sized arrays to be returned, or a sequence of indices at which to split the array.
  • axis : The axis along which to split. Default is 0.


import numpy as np 
# Create an array 
array = np.arange(12)
print("Original array:\n", array) 

# Split the array into 3 equal parts 
split_array = np.split(array, 3)
print("Split into 3 arrays:", split_array) 

Horizontal and Vertical Splitting: np.hsplit and np.vsplit

For higher-dimensional arrays, it's often necessary to split along different axes. This is where np.hsplit and np.vsplit come into play.

Horizontal Splitting (np.hsplit)

np.hsplit is used to split an array into multiple sub-arrays horizontally (column-wise).

# Create a 2D array 
array2d = np.arange(16).reshape(4, 4)
print("Original 2D array:\n", array2d)
#Split the array into 2 

horizontally hsplit_array = np.hsplit(array2d, 2)
print("Horizontally split arrays:", hsplit_array) 

Vertical Splitting (np.vsplit)

np.vsplit splits an array into multiple sub-arrays vertically (row-wise).

# Split the array into 2 vertically 
vsplit_array = np.vsplit(array2d, 2)
print("Vertically split arrays:", vsplit_array) 

Other Splitting Functions: np.array_split

Sometimes, you need to split arrays into sub-arrays of unequal size, which is where np.array_split becomes useful.

# Split the array into 3 parts of unequal size 
array_split_array = np.array_split(array, 3)
print("Unequally split arrays:", array_split_array) 

Practical Considerations

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  1. Shape Compatibility : Make sure the array can be divided into the desired number of sub-arrays. Otherwise, NumPy will raise an error.
  2. Unequal Splitting : Use np.array_split when you need sub-arrays of unequal sizes.
  3. Axis Parameter : Pay attention to the axis along which you're splitting, especially in multi-dimensional arrays.
  4. Memory Management : Splitting large arrays can consume a significant amount of memory, so it should be done with care.


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Array splitting in NumPy is a powerful feature that can be used for a variety of tasks in data analysis and machine learning. Whether you need to divide data into test and train sets, process information in chunks, or simply organize your datasets, the splitting functions in NumPy offer a fast and efficient solution. With the knowledge of np.split , np.hsplit , np.vsplit , and np.array_split , you can handle any array splitting task with ease.