Flattening Arrays

Flattening an array means converting it from a multi-dimensional array into a 1D array, essentially unraveling its contents.

This operation is useful when you need to process the elements of an array one by one or when you want to make data more suitable for certain algorithms.

There are three possible options for flattening in NumPy:

Using the ndarray.reshape(-1) method or the numpy.reshape(array, -1) function;
Using the ndarray.ravel() method or the numpy.ravel(array) function;
Using the ndarray.flatten() method.

reshape(-1)

The .reshape(-1) method or the reshape(array, -1) function will return a contiguous flattened array with the same number of elements.

As we have already mentioned in the previous chapter, -1 automatically calculates the size of the dimension based on the original array's size. Since we pass only a single integer for shape, a 1D array with the same number of elements is returned.

import numpy as np

array_2d = np.array([[1, 2, 3], [4, 5, 6]])

flattened_array = array_2d.reshape(-1)

print(f'Flatenned array: {flattened_array}')

# Changing the first element of flattened_array

flattened_array[0] = 10

print(f'Modified initial array:\n{array_2d}')


              1234567
            
import numpy as np
array_2d = np.array([[1, 2, 3], [4, 5, 6]])
flattened_array = array_2d.reshape(-1)
print(f'Flatenned array: {flattened_array}')
# Changing the first element of flattened_array
flattened_array[0] = 10
print(f'Modified initial array:\n{array_2d}')

The .reshape() method or the respective function returns a view of the original array, so any changes made to the reshaped array will also affect the original array.

Using flattened_array = np.reshape(array_2d, -1) can be used instead of calling the method.

ravel()

The ndarray.ravel() method or the numpy.ravel(array) function works the same as reshape(-1) and also returns a view of the original array:

import numpy as np

array_2d = np.array([[1, 2, 3], [4, 5, 6]])

flattened_array = array_2d.ravel()

print(f'Flatenned array: {flattened_array}')

# Changing the first element of flattened_array

flattened_array[0] = 10

print(f'Modified initial array:\n{array_2d}')


              1234567
            
import numpy as np
array_2d = np.array([[1, 2, 3], [4, 5, 6]])
flattened_array = array_2d.ravel()
print(f'Flatenned array: {flattened_array}')
# Changing the first element of flattened_array
flattened_array[0] = 10
print(f'Modified initial array:\n{array_2d}')

flattened_array = np.ravel(array_2d) can be used instead of calling the method.

ndarray.flatten()

In case you want a copy of the original array, not a view, you can use the .flatten() method:

import numpy as np

array_2d = np.array([[1, 2, 3], [4, 5, 6]])

flattened_array = array_2d.flatten()

print(f'Flatenned array: {flattened_array}')

# Changing the first element of flattened_array

flattened_array[0] = 10

print(f'Initial array:\n{array_2d}')


              1234567
            
import numpy as np
array_2d = np.array([[1, 2, 3], [4, 5, 6]])
flattened_array = array_2d.flatten()
print(f'Flatenned array: {flattened_array}')
# Changing the first element of flattened_array
flattened_array[0] = 10
print(f'Initial array:\n{array_2d}')

Note

You can always copy a view of an array to create a separate object and modify this copy without affecting the original array.

Tarea

Swipe to start coding

Use the .flatten() method correctly for flattening exam_scores and store the result in exam_scores_flattened.
Use the .reshape() method correctly for flattening exam_scores and store the result in exam_scores_reshaped.
Use the .ravel() method for flattening exam_scores and store the result in exam_scores_raveled.
Out of the three created flattened arrays, choose the one that is a copy of the original array, not a view, and assign 100 to its first element (use positive indexing).

Solución

import numpy as np

# Simulated exam scores for three students in three subjects

exam_scores = np.array([[75, 82, 90], [92, 88, 78], [60, 70, 85]])

# Use the flatten() method for flattening

exam_scores_flattened = exam_scores.flatten()

# Use the reshape() method for flattening

exam_scores_reshaped = exam_scores.reshape(-1)

# Use the ravel() method for flattening

exam_scores_raveled = exam_scores.ravel()

# Set the first element of the flattened copy to 100

exam_scores_flattened[0] = 100

print(exam_scores)

¿Todo estuvo claro?

¡Gracias por tus comentarios!

Sección 3. Capítulo 5

import numpy as np

# Simulated exam scores for three students in three subjects

exam_scores = np.array([[75, 82, 90], [92, 88, 78], [60, 70, 85]])

# Use the flatten() method for flattening

___ = ___

# Use the reshape() method for flattening

___ = ___

# Use the ravel() method for flattening

___ = ___

# Set the first element of the flattened copy to 100

___[___] = ___

print(exam_scores)