Map, Filter, Reduce and Lambda

Map

• map applies a function to all the items in an input list, and returns new list.

def double(x):
    return x * 2

numbers = [1, 2, 3, 4, 5]
doubles = list(map(double, numbers))
print(doubles)  # [2, 4, 6, 8, 10]

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Filter

• filter creates a list of elements for which a function returns True.

def is_even(x):
    return x % 2 == 0

numbers = [1, 2, 3, 4, 5]
evens = list(filter(is_even, numbers))
print(evens)  # [2, 4]

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Reduce

• reduce applies a rolling computation to sequential pairs of values in a list.

from functools import reduce

def add(x, y):
    return x + y

numbers = [1, 2, 3, 4, 5]
sum = reduce(add, numbers)
print(sum)  # 15

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Lambda

• lambda is an anonymous function that can have any number of arguments, but can have only one expression.

double = lambda x: x * 2
print(double(5))  # 10

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Using lambda function with map

numbers = [1, 2, 3, 4, 5]
doubles = list(map(lambda x: x * 2, numbers))
print(doubles)  # [2, 4, 6, 8, 10]