Video Link: https://youtu.be/kYIrDMbqunw
In this video, we learned how to use map() and filter() in Python with the help of examples.
Programs in the Video
The builtin functions like map() and filter() allow us to write simpler, shorter and more Pythonic code in place of
using loops and branching.
Let's first recap lambda functions.
Lambda functions are single-line functions defined without a name.
# def add(n1, n2):
# return n1 + n2
add = lambda n1, n2: n1 + n2
print(add(10, 20))Output
30
Suppose we have a list like this:
numbers = [1, 2, 3, 4, 5]We have to create a new list with all the squares of the numbers from this list.
For this, we would normally use a for loop and apply the square to each item:
numbers = [1, 2, 3, 4, 5]
squared_nums = []
square = lambda n: n ** 2
for num in numbers:
squared_nums.append(square(num))
print(squared_nums)Output
[1, 4, 9, 16, 25]
This same task can be done in a more elegant way using map():
numbers = [1, 2, 3, 4, 5]
squared_nums = map(lambda n: n ** 2, numbers)
print(squared_nums)Output
<map object at 0x7efd7e693070>
The map() function returns an iterator object. Let's use the list() function to convert this iterator back to a
list:
numbers = [1, 2, 3, 4, 5]
squared_nums = list(map(lambda n: n ** 2, numbers))
print(squared_nums)Output
[1, 4, 9, 16, 25]
We can also pass multiple iterable arguments to map():
num1 = [4, 5, 6]
num2 = [5, 6, 7]
result = map(lambda n1, n2: n1 + n2, num1, num2)
print(list(result))Output
[9, 11, 13]
The filter() function filters out only the elements for which the given function returns true:
numbers = [234, 3245, 639, 550, 654]
even_numbers = list(filter(lambda n: n % 2 == 0, numbers))
print(even_numbers)Output
[234, 550, 654]
- Use
map()to apply a function to each element of an iterable. - Use
filter()to filter out values of an iterable if they don't match the specified condition.