Reduce Function

The functools.reduce() function accumulates the results of applying a binary function to the items of an iterable, from left to right. It is similar to the #inject method in Ruby.

Ruby #inject example:

# Sum of elements in an array
array = [1, 2, 3, 4, 5]
sum = array.inject(0) { |result, element| result + element }
puts sum  # Output: 15

Equivalent Python code using functools.reduce():

from functools import reduce
my_list = [1, 2, 3, 4, 5]
sum_result = reduce(lambda result, element: result + element, my_list, 0)
print(sum_result)  # Output: 15

In this example, reduce() takes three arguments:

• A function (lambda function in this case) that specifies the operation to perform on each pair of elements.
• An iterable (list in this case) containing the elements to be processed.
• An optional initial value (0 in this case) for the accumulator.

The lambda function lambda result, element: result + element adds each element to the accumulated sum. The initial value 0 is specified as the third argument to reduce(), ensuring that the summation starts from zero.

The same with a function definition instead of a lambda:

from functools import reduce

def add(a, b):
    return a + b

my_list = [1, 2, 3, 4, 5]
sum_result = reduce(add, my_list, 0)
print(sum_result)  # Output: 15