Python | Remove None values from list
There can be multiple methods to remove None values from a Python list. Some of them are discussed as follows:
Method 1: Naive Method
In the naive method, we iterate through the whole list and append all the filtered, non-None values into a new list, hence ready to be performed with subsequent operations.
Python3
Output:
Time Complexity: O(n), where n is the length of the input list.
Auxiliary Space: O(n), as we’re using additional space res other than the input list itself with the same size of input list.
Method 2: Using list comprehension
The longer task of using the naive method and increasing line of codes can be done in a compact way using this method. We just check for not None values and construct the new filtered list.
How to Use Python to Remove Zeros from List
To remove zeros from a list using Python, the easiest way is to use list comprehension.
You can also use the Python filter() function.
When working with lists of numbers, it can be valuable to be able to easily filter and remove unwanted values from your list.
One such situation where you may want to remove values from a list is if you have a lot of zeros in your list.
We can easily remove all zeros from a list using Python with list comprehension. List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.
Below is the code which will allow you to remove all zeros from a list using list comprehension in Python.
Removing Zeros from List with Python filter() Function
The Python filter() function is a built-in function that allows you to process an iterable and extract items that satisfy a given condition.
We can use the Python filter() function to extract all the items in a list of numbers which do not equal 0 and remove the zeros from a list.
Below is some example code showing you how to remove zeros from a list using the filter() function.
Removing Any Value from List Using Python
In a very similar way, we can remove any value from a list using list comprehension.
For example, if we instead wanted to remove all of the ones from a list, we could do that easily with list comprehension in Python by adjusting the code above.
Another example would be if we have a list of strings, and we want to remove the word “whoa”, we can do that with list comprehension in Python.
Hopefully this article has been useful for you to learn how to remove zeros from a list in Python.
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Remove None from the List Python
Lists are used to store data of various types, and this data can be directly used for data analytics or for data processing purposes. The “None” in the list can cause severe ambiguities in the result of those operations, which is not what you want, do you? Well, this guide will use different methods and approaches to remove all of the “None” values from the list.
Listed below are all the different solutions that can be used to remove the None from the list in Python:
Solution 1: Using the remove() Method With the __contains__() Method
Whenever the user wants to remove an element, the very first method that comes to mind is the remove() method. However, the remove method cannot be used to remove all/multiple None values from the list. Because the remove() method only removes the first instance of the element from the list.
To demonstrate this, take the following code:
listVar = [ 69 , 22 , 65 ,None, None, 123 , 6789 ,None ]
listVar.remove ( None )
print ( listVar )
Executing this code will produce the following result on the terminal of your machine:
The output confirms that only the first instance of “None” was removed. To remove all the instances of the “None” from the list, use the while loop along with the __contains__() method:
listVar = [ 69 , 22 , 65 ,None, None, 123 , 6789 ,None ]
while listVar.__contains__ ( None ) :
listVar.remove ( None )
print ( listVar )
In this code snippet, the while loop keeps running until there are no more instances of “None” left in the list. When this code is executed, it produces the following result on the terminal:
The output confirms that there are no more instances of “None” found in the list, meaning all of them have been removed successfully.
Solution 2: Using List Comprehension With If-Condition
Another way of removing the “None” from the list is by using the list comprehension to go through every element, comparing it with “None” through the if-condition, and placing the non-None values in a separate list.
To remove None from the list using this method, take the following code snippet:
listVar = [ 69 , 22 , 65 ,None, None, 123 , 6789 ,None ]
newList = [ ]
for x in listVar:
if x is not None:
newList.append ( x )
print ( "Original List: " ,listVar )
print ( "New List: " ,newList )
When this code is executed, it will produce the following outcome on the terminal of your machine:
The output confirms that there are no “None” values present in the new list.
Solution 3: Using the Filter() Method to Remove None Values From List
The filter() method can also be used to remove “None” from a list, but using it normally can cause some issues. The filter() method considers the value “0” as “None”, and removes that from the list as well. To demonstrate this, take the following piece of code:
listVar = [ 69 , 0 , 22 , 65 , 0 ,None, None, 123 , 6789 ,None ]
res = list ( filter ( None, listVar ) )
print ( "Original List: " , listVar )
print ( "List After Filter: " ,res )
When this code is executed, it will produce the following result on your terminal:
From the output, it can be clearly observed that the filter() method has also removed the value “0” from the list.
The correct way to use the filter() method to remove all the “None” values from the list without interrupting other values of the list is to use a “Lambda Statement” within the first argument:
listVar = [ 69 , 0 , 22 , 65 , 0 ,None, None, 123 , 6789 ,None ]
res = list ( filter ( lambda elem: elem is not None, listVar ) )
print ( "Original List: " , listVar )
print ( "List After Filter: " ,res )
This time around when the code is executed, it will produce the following output on the terminal:
As you can see, you have successfully removed all the “None” values from the list successfully using the filter() method.
Conclusion
The user can remove all the “None” values from a Python list by using the remove() method along with the __contains__() method, list comprehension with if-condition, or by using the filter() method with lambda statement. All of these three methods have been thoroughly elaborated in this post with pictorial representation.
About the author
Abdul Mannan
I am curious about technology and writing and exploring it is my passion. I am interested in learning new skills and improving my knowledge and I hold a bachelor’s degree in computer science.
Удалить пустые строки из списка строк в Python
В этом посте мы обсудим, как удалить пустые строки из списка строк в Python.
1. Использование filter() функция
Рекомендуемое решение — использовать встроенную функцию filter(function, iterable) , который строит iterator из элементов iterable для которого указано функция возвращает истину. Если функция None , предполагается тождественная функция, т. е. все элементы iterable, которые являются ложными, удаляются. Вот рабочий пример с использованием фильтров:
Вы также можете пройти len функция для фильтрации пустых строк из списка, как показано ниже:
2. Использование понимания списка
Вы также можете использовать понимание списка для удаления пустых строк из списка строк. Понимание списка состоит из выражения, за которым следует цикл for, за которым следует необязательный цикл for или оператор if, заключенные в квадратные скобки. [] . Обратите внимание, что это решение медленнее, чем подход с фильтром.
3. Использование join() с split() функция
Выражение ‘ ‘.join(iterable).split() может использоваться для фильтрации пустых значений из итерации. ‘ ‘.join(list) эффективно объединить список строк, разделенных пробелом. затем split() Функция вызывается для результирующей строки, которая возвращает список строк, в которых последовательные пробелы считаются одним разделителем.