Remove elements from list based on a condition in Python

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Borislav Hadzhiev

Last updated: Aug 16, 2022

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Remove elements from list based on a condition in Python #

Use a list comprehension to remove elements from a list based on a condition, e.g. new_list = [item for item in my_list if item > 100]. The list comprehension will return a new list that doesn't contain any of the elements that don't meet the condition.

main.py
my_list = [22, 55, 99, 105, 155, 205] # ✅ remove elements from list based on condition (list comprehension) new_list = [item for item in my_list if item > 100] print(new_list) # 👉️ [105, 155, 205] # ---------------------------------------- # ✅ remove elements from list based on condition (using filter) new_list = list(filter(lambda item: item > 100, my_list)) print(new_list) # 👉️ [105, 155, 205] # ---------------------------------------- # ✅ remove elements from list based on condition (using for loop) for item in my_list.copy(): if item <= 100: my_list.remove(item) print(my_list) # 👉️ [105, 155, 205]

The first example uses a list comprehension to remove elements from a list based on a condition.

List comprehensions are used to perform some operation for every element or select a subset of elements that meet a condition.
main.py
my_list = [22, 55, 99, 105, 155, 205] new_list = [item for item in my_list if item > 100] print(new_list) # 👉️ [105, 155, 205]

On each iteration, we check if the current list item is greater than 100 and return the result.

The new list will only contain values that are greater than 100.

The list comprehension doesn't change the original list, it creates a new list.

If you need to change the original list, use a list slice.

main.py
my_list = [22, 55, 99, 105, 155, 205] my_list[:] = [item for item in my_list if item > 100] print(my_list) # 👉️ [105, 155, 205]

We used the my_list[:] syntax to get a slice that represents the entire list, so we can assign to the variable directly.

The slice my_list[:] represents the entire list, so when we use it on the left-hand side, we are assigning to the entire list.

This approach changes the contents of the original list.

Alternatively, you can use the filter() function.

Remove elements from list based on a condition using filter() #

To remove elements from a list based on a condition:

  1. Use the filter() function to filter out elements that don't meet the condition.
  2. Use the list() class to convert the filter object to a list.
  3. The new list won't contain any elements that don't meet the condition.
main.py
my_list = [22, 55, 99, 105, 155, 205] new_list = list(filter(lambda item: item > 100, my_list)) print(new_list) # 👉️ [105, 155, 205]

We used the filter() function to remove elements from a list based on a condition.

The filter function takes a function and an iterable as arguments and constructs an iterator from the elements of the iterable for which the function returns a truthy value.

The lambda function gets called with each element in the list, checks if the value is greater than 100 and returns the result.

The filter object only contains values that are greater than 100.

The last step is to use the list() class to convert the filter object to a list.

Alternatively, you can use a for loop.

Remove elements from list based on a condition using for loop #

To remove elements from a list based on a condition:

  1. Use a for loop to iterate over a copy of the list.
  2. On each iteration, check if the current item meets a condition.
  3. Use the list.remove() method to remove the matching elements.
main.py
my_list = [22, 55, 99, 105, 155, 205] for item in my_list.copy(): if item <= 100: my_list.remove(item) print(my_list) # 👉️ [105, 155, 205]
On each iteration, we check if the current item is less than or equal to 100 and use the list.remove() method to remove the matching elements.

The list.remove() method removes the first item from the list whose value is equal to the passed in argument.

The remove() method mutates the original list and returns None.

The most important thing to note when removing items from a list in a for loop is to use the list.copy() method to iterate over a copy of the list.

If you try to iterate over the original list and remove items from it, you might run into difficult to locate bugs.

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