Methods on NumPy.add()

The ufunc expect a set of scalars as input and produce a set of scalars as output. Universal
functions can be related to mathematical aspects such as, add, subtract, divide, multiply, and likewise.

Methods on numpy.add

Actually, universal functions are not functions instead, these are objects representing functions. Here we are taking the function – add, they have two input parameters and return one output parameter (signature mismatch of ufunc will results in a ValueError. Hence this will work only for binary universal functions).

The four methods on add are:

• reduce
• accumulate
• outer
• reduceat

In this tutorial we are going through each of the above function in detail.

numpy.ufunc.reduce()

The given input array is reduced by applying the universal function recursively along a specified axis on consecutive elements.
Note: add.reduce() is equivalent to sum()

Syntax: ufunc.reduce(a, axis=0, dtype=None, out=None, keepdims=False, initial=, where=True)

Parameters:
a(array_like): The array upon which processing occurs
axis(None or int or tuple of ints, optional): Axis or axes along which a reduction is performed. The default is (axis = 0). Axis may be negative, whenever it counts backwards.None, a reduction is performed over all the axes.Tuple of ints, a reduction is performed on multiple axes.
dtype(data-type code, optional): The type used to represent the intermediate results.
out(ndarray, None, or tuple of ndarray and None, optional): Location into which the result is stored. If not provided or None, a freshly-allocated array is returned.
keepdims(bool, optional): If this is set to True, the axes which are reduced are left in the result as dimensions with size one.
initial(scalar, optional): The value with which to start the reduction.
where(array_like of bool, optional): A boolean array which is broadcasted to match the dimensions of a, and selects elements to include in the reduction.

Returns:
r : ndarray

Example:

# Reducing an array using np.add.reduce()

import numpy as np


# Array formation
a = np.arange(10)

# Reduction occurs column-wise with
# 'int' datatype
b = np.add.reduce(a, dtype = int, axis = 0)
print("The array {0} gets reduced to {1}".format(a, b))

OUTPUT

The array [0 1 2 3 4 5 6 7 8 9] gets reduced to 45

numpy.ufunc.accumulate()

It stores the intermediate results in an array and returns that. The result, in the case of the add function, is equivalent to calling the cumsum function.

Syntax: ufunc.accumulate(array, axis=0, dtype=None, out=None)

Parameters:
array(array_like): The array to act on.
axis(int, optional): The axis along which to apply the accumulation; default is zero.
dtype(data-type code, optional): The data-type used to represent the intermediate results. Defaults to the data-type of the output array if such is provided, or the data-type of the input array if no output array is provided.
out(ndarray, optional): A location into which the result is stored. If not provided a freshly-allocated array is returned.

Returns:
r : ndarray

Example:

import numpy as np


# Array formation
a = np.arange(10)

# Cumulative sum of array, column wise,
# float datatype
c = np.add.accumulate(a, axis = 0, dtype = float)

print("The array {0} gets added cumulatively to {1}".format(a, c))

OUTPUT

The array [0 1 2 3 4 5 6 7 8 9] gets added cumulatively to [ 0. 1. 3. 6. 10. 15. 21. 28. 36. 45.]

numpy.ufunc.outer()

The ‘outer’ method returns an array that has a rank, which is the sum of the ranks of its two input arrays. The method is applied to all possible pairs of the input array elements.

Syntax: ufunc.outer(A, B, **kwargs)

Parameters:
A(array_like): First array
B(array_like): Second array
kwargs(any): Arguments to pass on to the ufunc.

Returns:
r : ndarray

Example:

# To find the outer of two input arrays
import numpy as np


# Initialization of a 2x2 matrix
# as first input
a = np.arange(4).reshape(2,2)

# Initialization of an array as
# second input
b = np.arange(3)

# Outer of a & b
z = np.add.outer(b, a)

print("The outer of {0} & {1} is {2}".format(b,a,z))

OUTPUT

The outer of [0 1 2] & [[0 1]
 [2 3]] is [[[0 1]
  [2 3]]

 [[1 2]
  [3 4]]

 [[2 3]
  [4 5]]]

numpy.ufunc.reduceat()

The ‘reduceat()‘ method requires as arguments, an input array, and a list of indices. The reduceat() method goes through step-by-step procedures to perform its operation. We will look up its action by four steps.

Example:

# Reduceat method example

import numpy as np


a = np.arange(9)
z = np.add.reduceat(a, [1, 4, 2, 8])

print("Reduceat of matrix {} is {}".format(a,z))

OUTPUT

Reduceat of matrix [0 1 2 3 4 5 6 7 8] is [ 6 4 27 8]

STEP-1
It concerns with indices 1 and 4. This step results in a reduced operation of the array elements between indices 1 and 4.

import numpy as np


a = np.arange(9)
print("Result of STEP-I is", np.add.reduce(a[0:4]))

OUTPUT

Result of STEP-I is 6

STEP-2
The second step concerns indices 4 and 2. Since 2 is less than 4, the array element at index 4 is returned:

import numpy as np


a = np.arange(9)
print("Result of STEP-II is", a[4])

OUTPUT

Result of STEP-II is 4

STEP-3
The third step concerns indices 2 and 8. This step results in a reduce operation of the array elements between indices 2 and 8:

import numpy as np


a = np.arange(9)
print("Result of STEP-III is", np.add.reduce(a[2:8]))

OUTPUT

Result of STEP-III is 27

STEP-4
The fourth step concerns index 8. This step results in a reduce operation of the array elements from index 8 to the end of the array:

import numpy as np


a = np.arange(9)
print("Result of step IV is", np.add.reduce(a[8:]))

OUTPUT

Result of step IV is 8

By going through all this step we get the output of ‘numpy.add.reduceat’.