Lambda, Map, and Filter in Python

Lambda: Lambda functions are known as the anonymous functions in Python. This kind of functions are declared without any name.

• Can accept any number of argument. 
• Restricted to only a single expression. 
• Used only one-time.
• Lambda function is used when you need a function for a short period of time. 

Basic syntax: 

lambda arguments : expression

Example:

	# A lambda function that multiplies two numbers
	multiply = lambda x, y: x * y
	print(multiply(2, 2)) # output: 4
	# A lambda function that multiplies three numbers
	multiply = lambda x, y, z: x * y * z
	print(multiply(2, 2, 2)) # output: 8
	# A lambda function that adds 10 to the number passed in as an argument, and print the resul
	a = lambda a: a + 10
	print(a(5)) # output: 15

view raw Lambda.py hosted with ❤ by GitHub

Map: Map is a built-in function that takes a function object and iterable list (list/dictionary) as its parameter.
Basic syntax:
map (function_object, iterable_1, iterable_2, ... )

Few examples of Map in python:

	def add_t(x):
	return x + 1
	tuple_1 = (1, 2, 3, 4)
	map_sample_1 = tuple(map(add_t, tuple_1))
	print(map_sample_1) # output: (2, 3, 4, 5)
	# ---------------------------------------------------------------
	def add_one(x):
	return x + 1
	list_2 = [1, 2, 3, 4]
	map_sample_2 = list(map(add_one, list_2))
	print(map_sample_2) # output: [2, 3, 4, 5]
	# ---------------------------------------------------------------------
	list_sample = [1, 2, 3, 4]
	map_sample = list(map(lambda x: x + 1, list_sample))
	print(map_sample) # output: [2, 3, 4, 5]
	# ----------------------------------
	def func(x):
	return x + 1
	my_dictionary = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
	my_dictionary = dict(
	map(lambda kv: (kv[0], func(kv[1])), my_dictionary.items()))
	print(my_dictionary) # output: {'a': 2, 'b': 3, 'c': 4, 'd': 5}

view raw Map.py hosted with ❤ by GitHub

Filter: It works similar way like map. The difference is it makes a new list from the element in the list that satisfy some condition. In case of of parameters, it takes a function and one iterable.
Basic syntax:
filter (function, iterable)

Normally used with lambda functions. Example is given below:

	seq = [1, 2, 3, 4]
	# result contains odd numbers of the list
	result = filter(lambda x: x + 1, seq)
	print(list(result)) # Output: [1, 2, 3, 4]
	# Does nothing on seq as the lambda function does not hold any condition
	# filter only works on condition, so we need to give some conditional statement with lambda
	result = filter(lambda x: x % 2 == 0,
	seq) # returns the elements which are only divisible by two
	print(list(result)) # output: [2, 4]

view raw Filter.py hosted with ❤ by GitHub