NumPy stack Step-by-Step Examples

NumPy, the fundamental package for scientific computing in Python, provides a powerful array manipulation library that is essential for data analysis and machine learning tasks. Among its plethora of functions, the 'stack()' function stands out as a versatile tool for combining arrays along a specified axis. In this blog post, we'll delve into the intricacies of NumPy 'stack()' function, exploring its syntax, use cases, and providing step-by-step examples to solidify your understanding. 


Understanding the 'stack()' Function:

The 'stack()' function in NumPy is primarily used for stacking arrays along a new axis. It allows you to concatenate arrays along a new axis, either horizontally (axis=1) or vertically (axis=0). This capability is particularly useful when dealing with multi-dimensional arrays or combining multiple arrays to form a new one.

Syntax of 'stack()':

The syntax of the 'stack()' function is as follows:

numpy.stack(arrays, axis=0, out=None)

  • arrays: A sequence of arrays to be stacked. These should have the same shape along all axes except the one specified by 'axis'.
  • axis (optional): The axis along which the arrays will be stacked. Default is '0'.
  • out (optional): If provided, the destination array for the stacked result. It must have the correct shape and type.

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Step-by-Step Examples:

Example 1: Vertical Stack

Let's start with a simple example of stacking two one-dimensional arrays vertically.

import numpy as np

arr1 = np.array([11, 32, 13])
arr2 = np.array([34, 55, 16])

result = np.stack((arr1, arr2), axis=0)

print("Vertical Stack Result:")


Vertical Stack Result:
[[11 32 13]
 [34 55 16]]




Example 2: Horizontal Stack

Now, let's explore a horizontal stack example with two one-dimensional arrays.

import numpy as np

arr1 = np.array([11, 32, 13])
arr2 = np.array([34, 55, 16])

result = np.stack((arr1, arr2), axis=1)

print("Horizontal Stack Result:")


Horizontal Stack Result:
[[11 34]
 [32 55]
 [13 16]]

Example 3: Stacking Along a New Axis

In this example, we'll stack two two-dimensional arrays along a new axis.

import numpy as np

arr1 = np.array([[11, 52, 13], [24, 65, 66]])
arr2 = np.array([[71, 28, 99], [101, 11, 32]])

result = np.stack((arr1, arr2), axis=2)

print("Stack Along New Axis Result:")


Stack Along New Axis Result:
[[[ 11  71]
  [ 52  28]
  [ 13  99]]

 [[ 24 101]
  [ 65  11]
  [ 66  32]]]


NumPy's stack() function is a powerful tool for array manipulation, offering flexibility in combining arrays along specified axes. By mastering its usage through step-by-step examples, you can enhance your proficiency in data analysis and machine learning workflows. Experiment with various scenarios to unlock the full potential of the 'stack()' function in your Python programming endeavors.

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