The filter() function in Python
The filter() function is used to filter elements from an iterable based on a condition.
Syntax
function: A function that returns True or False.
iterable: The list (or tuple, etc.) to filter.
It returns a filter object, which you can convert to a list, set, or tuple.
Example
Let’s say we want to filter out only even numbers from a list.
Without filter():
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
even_numbers = []
for num in numbers:
if num % 2 == 0:
even_numbers.append(num)
print(even_numbers)
[2, 4, 6, 8]
With filter():
[2, 4, 6, 8]
Using named functions:
We can also use named functions instead of lambda functions, as of the example below
def is_even(num):
return num % 2 == 0
even_numbers = filter(is_even, numbers)
print(list(even_numbers))
[2, 4, 6, 8]
Using filter() with strings:
In the example below, we filter out the "short" words from the list of words
words = ['data', 'ai', 'machine', 'learning']
long_words = filter(lambda word: len(word) > 4, words)
print(list(long_words))
['machine', 'learning']
Using filter() to clean data:
In the example below, we remove all the None values from the list
data = [10, None, 25, None, 40, 0]
cleaned = filter(lambda value: value is not None, data)
print(list(cleaned))
[10, 25, 40, 0]