Python NumPy diff() Function

Diff() function python – Python NumPy diff() Function

by

NumPy diff() Function:

Diff() function python: The diff() function of the numpy module is used for calculating the nth discrete difference along the specified axis.

The first difference is given by out[i] = a[i+1] – a[i] along the specified axis, higher differences are calculated recursively by this function.

Syntax:

numpy.diff(a, n=1, axis=-1, prepend=<no value>, append=<no value>)

Parameters

a: This is required. It is an array (array-like) given as input.

n: This is optional. It indicates the number of times values are differenced. If the value is 0, the input is returned unchanged.

axis: This is optional. It indicates the axis along which the difference is calculated; the last axis is the default.

prepend, append: This is optional. Before conducting the difference, give the values to prepend or append to along the axis. Scalar values are expanded to arrays of length 1 in the axis direction and the shape of the input array in all other axes. Otherwise, the dimension and shape must be identical with “a” except along the axis.

Return Value: 

Numpy diff: An array with n-th discrete difference along the specified axis of “a” is returned. The output has the same shape as a, except along the axis where the dimension is smaller by n.

NumPy diff() Function in Python

Example1

Approach:

  • Import NumPy module using the import keyword.
  • Pass some random list as an argument to the array() function to create an array.
  • Store it in a variable.
  • Print the above-given array.
  • Get the first difference array by passing the given array and 1 as arguments the diff() function.
  • To get the second difference array we apply the diff() function for the above result and pass second argument as 1.
  • We can directly get the second difference array by passing 2 as the second arguments to the diff() function.
  • Print the first difference array.
  • Print the second difference array from the first difference array.
  • Print the second difference array directly.
  • The Exit of the Program

Below is the implementation:

# Import NumPy module using the import keyword.
import numpy as np
# Pass some random list as an argument to the array() function to
# create an array. 
# Store it in a variable.                   
gvn_arry = np.array([5, 10, 12, 4, 25])
# Print the above given array.
print("The above given array is:")
print(gvn_arry)
# Get the first difference array by passing the given array and 1 as 
# argument the diff() function.
fst_diffrnce = np.diff(gvn_arry, 1)
# To get the second difference array we apply the diff() function for the
# above result and pass second argument as 1
scnd_diffrnce = np.diff(fst_diffrnce, 1)

# We can directly get the second difference array by passing 2 as second argument to
# the diff() function
direct_scnddiff = np.diff(gvn_arry, 2)
# Print the first difference array
print("The first difference array:", fst_diffrnce)
# Print the second difference array from first difference array
print("The second difference array from first difference array:", scnd_diffrnce)
# Print the second difference array directly
print("The second difference array directly :", direct_scnddiff)

Output:

The above given array is:
[ 5 10 12 4 25]
The first difference array: [ 5 2 -8 21]
The second difference array from first difference array: [ -3 -10 29]
The second difference array directly : [ -3 -10 29]

Example2

Approach:

  • Import NumPy module using the import keyword.
  • Pass some random list as an argument to the array() function to create an array.
  • Store it in a variable.
  • Print the above-given array.
  • Get the first difference array along axis=0 by passing the given array, 1 and axis=0 as arguments the diff() function.
  • To get the first difference array along axis=1, apply the diff() function by # passing the given array, 1 and axis=1 as the arguments to it.
  • Print the first difference array along axis= 0.
  • Print the first difference array along axis= 1.
  • The Exit of the Program.

Below is the implementation:

# Import NumPy module using the import keyword.
import numpy as np
# Pass some random list as an argument to the array() function to
# create an array. 
# Store it in a variable.                   
gvn_arry = np.array([[2, 5, 8], 
                     [1, 3, 2],
                     [4, 6, 5]])
# Print the above given array.
print("The above given array is:")
print(gvn_arry)
# Get the first difference array along axis=0 by passing the given array, 1 and axis=0 as 
# arguments the diff() function.
fst_diffrnce_0 = np.diff(gvn_arry, 1, axis=0)
# To get the first difference array along axis=1, apply the diff() function by 
# passing the given array, 1 and axis=1 as the arguments to it.
fst_diffrnce_1 = np.diff(gvn_arry, 1, axis=1)

# Print the first difference array along axis= 0
print("The first difference array along axis= 0:\n", fst_diffrnce_0)
# Print the first difference array along axis= 1
print("The first difference array along axis= 1:\n", fst_diffrnce_1)

Output:

The above given array is:
[[2 5 8]
[1 3 2]
[4 6 5]]
The first difference array along axis= 0:
[[-1 -2 -6]
[ 3 3 3]]
The first difference array along axis= 1:
[[ 3 3]
[ 2 -1]
[ 2 -1]]