In this article, we will discuss how to filter a python list by using predicate. Filter function is used to filter the elements in the given list of elements with the help of a predicate. A predicate is a function that always returns True or False by performing some condition operations in a filter method
Syntax:
filter(predicate, list)
where,
- list is an input list
- predicate is the condition to be performed on the given list
Method 1: Using lambda as predicate
Here lambda is used to evaluate an expression that acts as a predicate.
Syntax:
filter(lambda x: condition, list)
where
- list is an input list
- condition act as predicate
Example: Filter all even numbers and odd numbers in a list
Python3
# create a list of 10 elements data = [10, 2, 3, 4, 56, 32, 56, 32, 21, 59] # apply a filter that takes only even numbers with # lambda as predicate a = filter(lambda x: x % 2 == 0, data) # display for i in a: print(i) print("------------") # apply a filter that takes only odd numbers with # lambda as predicate a = filter(lambda x: x % 2 != 0, data) # display for i in a: print(i) |
Output:
10 2 4 56 32 56 32 ------------ 3 21 59
Method 2: Using list comprehension
Here list comprehension act as a predicate.
Syntax:
[iterator for iterator in list condition]
where,
- list is the input list
- iterator is used to iterate the input list of elements
- condition act as predicate
Example: Python code to get odd and even numbers
Python3
# create a list of 10 elements data = [10, 2, 3, 4, 56, 32, 56, 32, 21, 59] # filter data using comprehension # to get even numbers print([x for x in data if x % 2 == 0]) # filter data using comprehension # to get odd numbers print([x for x in data if x % 2 != 0]) |
Output:
[10, 2, 4, 56, 32, 56, 32] [3, 21, 59]