Python Map, Filter & Reduce pythonocean python ocean

The map() Function

The map() function iterates through all items in the given iterable i.e list etc and executes the function we passed as an argument.

The syntax is of map() function is following:

map(function, iterable(s))

Example of map is following

def filter_even_numbers(s):
    if s%2==0:
        return s
nums = [2,3,4,5,6]
map_object = map(filter_even_numbers, nums)
print(list(map_object))
## It will output an array with values : [2,None,4,None,6]

 Above code will filter out even numbers and print them out.

The Filter() Function

Similar to map() function, filter() takes a function object and creates a new list.

As the name suggests, filter() create a new list that contains only elements that satisfy a certain condition.

Syntax is following

filter(function, iterable(s))

def filter_even_numbers(s):
    if s%2==0:
        return s
nums = [2,3,4,5,6]
map_object = filter(filter_even_numbers, nums)
list(map_object)
## It will output an array with values : [2,4,6]

The Reduce Function() 

Reduce () works differently from map () and filter (). It does not return any new list based on function and what we have passed is repetitive. Instead, it returns a single value.

In addition, reduce () in Python 3 no longer has the built-in function, and it can be found in the Functools module.

from functools import reduce

def add(x, y):
    return x + y
list = [3, 8, 10]
print(reduce(add, list))
## It will output sum of elements of list that is 21