filter() python - Python : filter() function | Tutorial and Examples

filter() function in Python

filter() python: This article is about using filter() with lambda.

filter() function :

Python filter function: This filter() function is used to filter some content from a given sequence where the sequence may be a list, tuple or string etc.

Syntax : filter(function, iterable)

where,

function refers to a function that accepts an argument and returns bool i.e True or False based on some condition.
iterable refers to the sequence which will be filtered.

How it works ?

Actually filter() function iterates over all elemnts of the sequence and for each element the given callback function is called.

If False is returned by the function then that element is skipped.
If True is returned by the function then that element is added into a new list.

Filter a list of strings in Python using filter() :

#Program :

# A list containg string as elemnt
words = ['ant', 'bat', 'dog', 'eye', 'ink', 'job']

# function that filters words that begin with vowel
def filter_vowels(words):
    vowels = ['ant', 'eye', 'ink']

    if(words in vowels):
      return True
    else:
      return False

filtered_vowels = filter(filter_vowels, words)


# Print words that start with vowel
print('The filtered words are:')
for vowel in filtered_vowels:
print(vowel)

Output :
ant
eye
ink

In the above example we had created one separate function as filtered_vowels and we passed it to filter() function.

Using filter() with Lambda function :

In this we will pass an lambda function rather passing a separate function in filter() function. And the condition is to select words whose length is 6.

So, let’s see an example of it.

#Program :

# A list containg string as elemnt
words = ['ant', 'basket', 'dog', 'table', 'ink', 'school']

#It will return string whose length is 6
filtered_vowels = list(filter(lambda x : len(x) == 6 , words))


# Print words that start with vowel
print('The filtered words are:')
for vowel in filtered_vowels:
    print(vowel)

Output :
The filtered words are:
basket
school

Filter characters from a string in Python using filter() :

Now, let’s take example how to filter a character in a string and remove that character in the string.

#Program :

# A list containg string as elemnt
str_sample = "Hello, you are studying from Btech Geeks."

#It will return particular character in the string
#then those chharacters are removed from the string
filteredChars = ''.join((filter(lambda x: x not in ['e', 's'], str_sample)))


# Print the new string 
print('Filtered Characters  : ', filteredChars)

Output : 
Hllo, you ar tudying from Btch Gk.

Filter an array in Python using filter() :

Suppose we have an array. So, let’s see it how we can filter the elements from an array.

#Program :

# Two arrays 
sample_array1 = [1,3,4,5,21,33,45,66,77,88,99,5,3,32,55,66,77,22,3,4,5]
sample_array2 = [5,3,66]

#It will return a new array
#It will filter
#if array2 elemnts are present in array1 then that element will not be removed
filtered_Array = list(filter(lambda x : x not in sample_array2, sample_array1))
print('Filtered Array  : ', filtered_Array)

Output :

[1, 4, 21, 33, 45, 77, 88, 99, 32, 55, 77, 22 ,4]

filter() python – Python : filter() function | Tutorial and Examples