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Differences between Flatten() and Ravel() Numpy Functions

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  • Difficulty Level : Medium
  • Last Updated : 08 Nov, 2022
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We have two similar kinds of ways to convert a ndarray to a 1D array of Flatten() and Ravel() Numpy function in Python programming language.

Example of Flatten() Numpy function

Here, we will create a Numpy array, and then by using flatten function we have changed the element in the flattened 1D NumPy array.

Python3




import numpy as np
 
# Create a numpy array
a = np.array([(1,2,3,4),(3,1,4,2)])
 
# Let's print the array a
print ("Original array:\n ", a)
 
# Convert nd array to 1D array
c = a.flatten()
 
# Flatten passes copy of
# original array to 'c'
print ("\nFlatten array using flatten: ", c)

Output:

Original array:
  [[1 2 3 4]
 [3 1 4 2]]

Flatten array using flatten:  [1 2 3 4 3 1 4 2]

The original 2D array is unchanged even if the value of the second member in the flattened 1D Numpy array was changed. This demonstrates that flatten() does return a copy of the Numpy input array.

Python3




c[2] = 33
 
print ("Flatten array: ", c)
 
# Let's print the array a
print ("\nOriginal array:\n ", a)

Output:

Flatten array:  [ 1  2 33  4  3  1  4  2]

Original array:
  [[1 2 3 4]
 [3 1 4 2]]

Example of ravel() Numpy function

Here, we will create a Numpy array, and then by using the ravel() function we have changed the element in the flattened 1D NumPy array.

Python3




import numpy as np
 
# Create a numpy array
a = np.array([(1,2,3,4),(3,1,4,2)])
 
# Let's print the array a
print ("Original array:\n ", a)
 
ra = np.ravel(a)
print ("\nFlatten array using ravel: ", ra)

Output:

`Original array:
  [[1 2 3 4]
 [3 1 4 2]]

Flatten array using ravel:  [1 2 3 4 3 1 4 2]

As we can see, The original 2D array is changed if the value of the second member in the flattened 1D Numpy array was changed. This demonstrates that ravel() returns a shallow copy of the Numpy input array.

Python3




ra[3] = 44
 
print ("Flatten array: ", ra)
 
# Let's print the array a
print ("\nOriginal array:\n ", a)

Output:

Flatten array:  [ 1  2  3 44  3  1  4  2]

Original array:
  [[ 1  2  3 44]
 [ 3  1  4  2]]

Differences between Flatten() and Ravel()

ravel()

flatten()

Return only reference/view of the original arrayReturn copy of the original array
If you modify the array you would notice that the value of the original array also changes.If you modify any value of this array value of the original array is not affected.
Ravel is faster than flatten() as it does not occupy any memory.Flatten() is comparatively slower than ravel() as it occupies memory.
Ravel is a library-level function. Flatten is a method of an ndarray object. Let us check out the difference in this code.

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