map, filter & reduce in python

map, filter and reduce are the functions by which we can achieve functional programming in python.

map: This applied the function definition to each item in the input_list.

     map(function_to_be_applied, input_list)

Example : Squares of the elements in the input_list

items = [1, 2, 3, 4, 5]
squared = []
for i in items:
    squared.append(i*i)
print(squared)

items = [1, 2, 3, 4, 5]
print(list(map(lambda x: x*x, items)))

Result: [1, 4, 9, 16, 25]

filter: As the name suggests it just filters the original input_list according to the function definition and gives the output.

     filter(function_to_be_applied, input_list)

Example: Filter out the negative numbers in the list.

list = [1, -9, -3, 4, 5]
positiveNumbers = []
for i in list:
    if i > 0:
        positiveNumbers.append(i)
print(positiveNumbers)

list = [1, -9, -3, 4, 5]
print(list(filter(lambda x: x>0, list)))

Result: [1, 4, 5]

reduce: computatation will be performed on the sequential pairs of a list, and returns back single result unlike map and filter.

    reduce(function_to_be_applied, input_list)

Example: Calculate the element's sum in the list

input_list = [1, 2, 3, 4, 5]
sum = 0
for i in input_list:
    sum += i
print(sum)

import functools
input_list = [1, 2, 3, 4, 5]
sum = functools.reduce(lambda x,y: x+y, input_list)
print(sum)

Result: 15

There is an accumulate method which is there in itertools modules gives the similar results.

To check that out  Difference Between reduce & accumulate