Flatten A list of NumPy arrays

Prerequisite Differences between Flatten() and Ravel() Numpy Functions, numpy.ravel() in Python, 

In this article, we will see how we can flatten a list of numpy arrays. NumPy is a library for the Python programming language, adding support for large, multi-dimensional arrays and matrices, along with a large collection of high-level mathematical functions to operate on these arrays.

Flatten a list of NumPy array means to combine the multiple dimensional NumPy arrays into a single array or list, below is the example 

List of numpy array : 
[array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]]), 
array([[ 0.00353654]])]

Flatten numpy array : 
array([ 0.00353654, 0.00353654, 0.00353654, 0.00353654, 0.00353654, 
0.00353654, 0.00353654, 0.00353654, 0.00353654, 0.00353654, 
0.00353654, 0.00353654, 0.00353654]) 

Method 1
Using numpy’s concatenate method  

Python3

# importing numpy as np
import numpy as np

# list of numpy array
list_array = [np.array([[1]]),
               np.array([[2]]),
               np.array([[3]]),
               np.array([[4]]),
               np.array([[5]]),
               np.array([[6]]),
               np.array([[7]]),
               np.array([[8]]),
               np.array([[9]]),
               np.array([[10]]),
               np.array([[11]]),
               np.array([[12]]),
               np.array([[13]]),
               np.array([[14]]),
               np.array([[15]]),
               np.array([[16]])]

# concatenating all the numpy array
flatten = np.concatenate(list_array)

# printing the ravel flatten array
print(flatten.ravel())

Output :

[ 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16]

Method 2
Using numpy’s flatten method 

Python3

# importing numpy as np
import numpy as np

# list of numpy array
list_array = [np.array([[1]]),
               np.array([[2]]),
               np.array([[3]]),
               np.array([[4]]),
               np.array([[5]]),
               np.array([[6]]),
               np.array([[7]]),
               np.array([[8]]),
               np.array([[9]]),
               np.array([[10]]),
               np.array([[11]]),
               np.array([[12]]),
               np.array([[13]]),
               np.array([[14]]),
               np.array([[15]]),
               np.array([[16]])]

# flatten the numpy array
flatten = np.array(list_array).flatten()

# printing the flatten array
print(flatten)

Output :

[ 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16]

Method 3
Using numpy’s ravel method 

Python3

# importing numpy as np
import numpy as np

# list of numpy array
list_array = [np.array([[1]]),
               np.array([[2]]),
               np.array([[3]]),
               np.array([[4]]),
               np.array([[5]]),
               np.array([[6]]),
               np.array([[7]]),
               np.array([[8]]),
               np.array([[9]]),
               np.array([[10]]),
               np.array([[11]]),
               np.array([[12]]),
               np.array([[13]]),
               np.array([[14]]),
               np.array([[15]]),
               np.array([[16]])]

# flatten the numpy array using ravel method
flatten = np.array(list_array).ravel()

# printing the flatten array
print(flatten)

Output :

[ 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16]

Method 4
Using numpy’s reshape method  

Python3

# importing numpy as np
import numpy as np

# list of numpy array
list_array = [np.array([[1]]),
               np.array([[2]]),
               np.array([[3]]),
               np.array([[4]]),
               np.array([[5]]),
               np.array([[6]]),
               np.array([[7]]),
               np.array([[8]]),
               np.array([[9]]),
               np.array([[10]]),
               np.array([[11]]),
               np.array([[12]]),
               np.array([[13]]),
               np.array([[14]]),
               np.array([[15]]),
               np.array([[16]])]

# flatten the numpy array using reshape method
flatten = np.array(list_array).reshape(-1)

# printing the flatten array
print(flatten)

Output :

[ 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16]