How to Concatenate Arrays in Python (With Examples)

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The easiest way to concatenate arrays in Python is to use the numpy.concatenate function, which uses the following syntax:

numpy.concatenate((a1, a2, ….), axis = 0)

where:

• a1, a2 …: The sequence of arrays
• axis: The axis along which the arrays will be joined. Default is 0.

This tutorial provides several examples of how to use this function in practice.

Example 1: Concatenate Two Arrays

The following code shows how to concatenate two 1-dimensional arrays:

import numpy as np

#create two arrays
arr1 = np.array([1, 2, 3, 4, 5])
arr2 = np.array([6, 7, 8])

#concatentate the two arrays
np.concatenate((arr1, arr2))

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

The following code shows how to concatenate two 2-dimensional arrays:

import numpy as np

#create two arrays
arr1 = np.array([[3, 5], [9, 9], [12, 15]])
arr2 = np.array([[4, 0]])

#concatentate the two arrays
np.concatenate((arr1, arr2), axis=0)

array([[3, 5],
       [9, 9],
       [12, 15],
       [4, 0]])

#concatentate the two arrays and flatten the result
np.concatenate((arr1, arr2), axis=None)

array([3, 5, 9, 9, 12, 15, 4, 0])

Example 2: Concatenate More Than Two Arrays

We can use similar code to concatenate more than two arrays:

import numpy as np

#create four arrays
arr1 = np.array([[3, 5], [9, 9], [12, 15]])
arr2 = np.array([[4, 0]])
arr3 = np.array([[1, 1]])
arr4 = np.array([[8, 8]])

#concatentate all the arrays
np.concatenate((arr1, arr2, arr3, arr4), axis=0)

array([[3, 5],
       [9, 9],
       [12, 15],
       [4, 0],
       [1, 1],
       [8, 8]])

#concatentate all the arrays and flatten the result
np.concatenate((arr1, arr2, arr3, arr4), axis=None)

array([3, 5, 9, 9, 12, 15, 4, 0, 1, 1, 8, 8])

The following tutorials explain how to perform similar operations in NumPy: