Lambda Functions

lambda functions are anonymous functions
the lambda keyword is used to define an anonymous function
below is a lambda function named upper which takes a string as its argument and converts it to uppercase using the upper() method

s = 'n4jvp'
upper = lambda string: string.upper()
print(upper(s))

Lambda Function Syntax

a function can have any number of arguments but only one expression which is evaluated and returned
use lambda functions wherever function objects are required

lambda arguments : expression

Use of Lambda Function

condition checking using lambda function

format_numeric = lambda num: f"{num:e}" if isinstance(num, int) else f"{num:,.2f}"

print("Int formatting:", format_numeric(1000000))
print("float formatting:", format_numeric(999999.789541235))

Practical Uses of Python lambda function

Lambda Function with List Comprehension

on each iteration inside the list comprehension, a new lambda function with a default argument of x is created(where x is the current item in the iteration)
inside the for loop calling the same function object having the default argument using item() and get the desired value
is_even_list stores the list of lambda function objects

is_even_list = [lambda arg=x: arg * 10 for x in range(1, 5)]
for item in is_even_list:
    print(item())

Lambda Function with if-else

the Max lambda function to find the maximum of two integers

Max = lambda a, b : a if(a > b) else b
print(Max(1, 2))

Lambda with Multiple Statements

Lambda functions do not allow multiple statements
can create two lambda functions and then call the other lambda function as a parameter to the first function

a = [[2,3,4],[1, 4, 16, 64],[3, 6, 9, 12]]

sortList = lambda x: (sorted(i) for i in x)
secondLargest = lambda x, f : [y[len(y)-2] for y in f(x)]
res = secondLargest(a, sortList)

print(res)

Using lambda() Function with filter()

Filter out all odd numbers using filter() and lambda function

the filter() function takes a function and a list as arguments
the lambda function below returns True

lambda x: (x % 2 != 0)

causes filter method to add x to its internal list
when a has been iterated final_list is populated

filter out all the elements of a sequence 'sequence' for which the function returns True
code below returns the odd numbers from an input list

a = [5, 7, 22, 97, 54, 62, 77, 23, 73, 61]

final_list = list(filter(lambda x: (x % 2 != 0), a))
print(final_list)

Filter all people having age more than 18, using lambda and filter() function

code filters a list of ages and extracts the ages of adults (ages greater than 18)
prints the list of adult ages
the output displays the ages of individuals who are 18 years or older

ages = [13, 90, 17, 59, 21, 60, 5]
adults = list(filter(lambda age: age > 18, ages))

print(adults)

Using lambda() Function with map

the map() function takes in a function and a list as an argument
the function is called with a lambda function and a list
a new list is returned which contains all the lambda-modified items returned by that function for each item

Multiply all elements of a list by 2 using lambda and map() function

the code doubles each element in a list using a lambda function and the 'map' function
then prints the new list with the doubled elements

li = [5, 7, 22, 97, 54, 62, 77, 23, 73, 61]

final_list = list(map(lambda x: x*2, li))
print(final_list)

Transform all elements of a list to upper case using lambda and map() function

the code converts a list of animal names to uppercase using a lambda function and the 'map' function
then prints the list with the animal names in uppercase

animals = ['dog', 'cat', 'parrot', 'rabbit']
uppered_animals = list(map(lambda animal: animal.upper(), animals))

print(uppered_animals)animals = ['dog', 'cat', 'parrot', 'rabbit']
uppered_animals = list(map(lambda animal: animal.upper(), animals))

print(uppered_animals)

Using lambda() Function with reduce()

the reduce() function takes in a function and a list as an argument
the function is called with a lambda function and an iterable
a new reduced result is returned
performs a repetitive operation over the pairs of the iterable
the reduce() function belongs to the functools module

A sum of all elements in a list using lambda and reduce() function

the code calculates the sum of elements in a list using the 'reduce' function
it imports 'reduce' and defines a list
then applies a lambda function that adds two elements at a time
prints the sum of all elements in the list
output displays the computed sum

from functools import reduce
a = [5, 8, 10, 20, 50, 100]

total = reduce((lambda x, y: x + y), a)
print(total)

Find the maximum element in a list using lambda and reduce() function

the code uses the 'reduce' function to find the maximum element in a list
then prints the maximum element

import functools
a = [1, 3, 5, 6, 2, ]
print("The maximum element of the list is : ", end="")
print(functools.reduce(lambda i, j: i if i > j else j, a))