Remove items from a List while iterating using a list comprehension, Remove items from a List while iterating using filter(), Removing items from a List while iterating over it with range(), Removing items from a list while iterating with filterfalse(), remove items from a list while iterating over it, For or While loop to print Numbers from 1 to 10 in Python, Using multiple variables in a For loop in Python, Using a For or While Loop to take user input in Python, An integer representing the start of the range (defaults to, Go up to, but not including the provided integer, Range will consist of every N numbers from. 50 and remove the elements that meet the condition. Python Program to Remove All Occurrences of an Element in an Array/List, Python Remove Tuples from a List having every element as None, How to remove an element from an array in Java, Python Program to remove a specific digit from every element of the list. I can think of three approaches to solve your problem. How to remove an element from a list while traversing it? How to perfect forward variadic template args with default argument std::source_location? list. Method 1.> Use the framework that you had suggested (where one fills in a code inside a for loop). do_action(element) I use a small code with del to delete a tuple that meets the said condition. The range class is commonly used for looping a iterating. You can learn more about the related topics by checking out the following We make use of First and third party cookies to improve our user experience. This can be ensured using a return or a break. index, and the second is the item. It's simple and just another way to look at a problem @MarkAmery. We used the my_list[:] syntax to get a slice that represents the entire list. Return a deep copy of x. Method 1 and method 2 are faster than method 3. Feel free to change the list of tuples and the condition that I have chosen. Instead of a comprehension, you could also use itertools. the elements of the iterable for which the function returns a truthy value. Such as: Replacing a large sections of the list using a slice. "a, b" is not a tuple, but "(a, b)" is a tuple. so the 4th iteration done pointer moved onto the 5th Thats why your loop doesnt cover 65 since its moved into the previous index. @tonysepia glad to see this solution is still helpful :). To remove list elements while iterating over it: Use a for loop to iterate over a copy of the list. copy of the list by using In the final list we will only have those tuples whose sum is not equal to 15. enumerate gives you access to the item and the index at once. What should I use in place of code_to_remove_tup? We may sometimes need to remove an element from a list in Python. You could always iterate over a copy of the list, leaving you free to modify the original: for item in list(somelist): You can still use filter, moving to an outside function the element modification (iterating just once) def do_the_magic(x): Would it be possible for a civilization to create machines before wheels? It's easy to understand and appears to be overlooked by the contributors! If you need to mutate the original list, assign the result to a slice that From what I measured, NumPy starts to be faster for lists of more than 20 elements, and reaches >12x faster filtering for big lists of 1000 elements and more. I took this low-level approach. The filter function somelist[:] = (x for x in somelist if not check(x)) if e == Second is the list from which we want to delete elements It so Agree I had a use case where the list was quite long (110K items) and it was smarter to keep reducing the list instead. I needed to do something similar and in my case the problem was memory - I needed to merge multiple dataset objects within a list, after doing some stuff with them, as a new object, and needed to get rid of each entry I was merging to avoid duplicating all of them and blowing up memory. 2) The for loop will skip items in your list. list() class. Compare it, for instance, with: both of which make it crystal clear that you cannot modify a list being iterated except with the iterator itself, and gives you efficient ways to do so without copying the list. The list.copy method returns a shallow You should really just use comprehensions. c = [] do_action(x) This function removes the first occurrence of the element passed as argument in remove(). How to remove items from a list while iterating? Generally, if you are doing it quick and dirty and don't want to add a custom LinkedList class, you just want to go for the faster .append() option by default unless memory is a big concern. If you try to iterate over the original list and remove items from it, you might @Paul: Since dicts are unordered, slices are meaningless for dicts. You can use a list comprehension to create a new list containing only the elements you don't want to remove: somelist = [x for x in somelist if n Like enumerate(), you have to wrap it in list() to actually get a list out of it. i+=1 We can verify this with 'is' which is different from merely "equals" (==). And so if you are sure that you really do want the code pattern described in the original question, it is possible. In my case I need to move those 'unwanted' elements into another list. You should NEVER delete an element from a list while iterating over it in a for loop. This approach achieves the same result as using the. I couldn't understand any answers before this one. returns an enumerate object containing tuples where the first element is the This is the right answer if performance is an issue (although same as @Alexey). The original fluidL object would still be used by the for loop but would become out of scope for us to modify. It's less condensed for those people that don't like compressed coding syntax. @Zen Because the second one iterates over a copy of the list. Is there a deep meaning to the fact that the particle, in a literary context, can be used in place of . You might also see examples that use the my_list[:] syntax to get a shallow Overview of workarounds Either: use a linked list implementation/roll your own. A linked list is the proper data structure to support efficient ite Filter receives a function and a sequence. In this case, each one is a tuple. Or the elements still in oldList that might be added next? Ok, I searched, what's this part on the inner part of the wing on a Cessna 152 - opposite of the thermometer, Calculating Triple Integral using Cylindrical Coordinates, If and When a Catholic Priest May Reveal Something from a Penitent's Confession. What I don't know is how efficient a couple of deletes are compared to copying a large list. How to remove an object from a list in Python? Iterators are sometimes better than sequences. How to remove element from list without using for loop? iteration. In Python 2: The answers suggesting list comprehensions are almost correctexcept that they build a completely new list and then give it the same name the old list as, they do not modify the old list in place. Find centralized, trusted content and collaborate around the technologies you use most. and to avoid having to re-code the entire project with the new lists name: copy.copy(x) @Alex Martelli's solution that already uses a list instead of a generator is most probably more efficient. The reversed() function: Unfortunately, I cannot adequately describe how reversed() works. This approach changes the contents of the original list. @MarkAmery don't think you can alter the list this way. Elegant way to remove items from sequence in Python? 587), The Overflow #185: The hardest part of software is requirements, Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g. left-hand side, we are assigning to the entire list. You can make a generator that returns everything that isn't removed: def newlist(somelist): List comprehensions are used to perform some operation for every element or select a subset of elements that meet a condition. The most important thing to note when removing items from a list in a for loop The list comprehension in the example doesn't mutate the original list. That's different from what you'd be doing by selective removal, as in Lennart's suggestionit's faster, but if your list is accessed via multiple references the fact that you're just reseating one of the references and not altering the list object itself can lead to subtle, disastrous bugs. I think this is very creative! This time efficient, but less space efficient because it keeps an extra copy of the array around during iteration. As I stated to start with: this is a complicated solution that will hurt the readability of your code and make it more difficult to debug. This means that if the suite deletes the current (or a previous) item from the sequence, the next item will be skipped (since it gets the index of the current item which has already been treated). Webplotly Remove Index from List in Python (2 Examples) In this tutorial, youll learn how to remove an element from a list by its index in Python. There might still be a way to use a list comprehension but it will begin to lose it's elegance, and for me it feels easier to modify a list in place. I needed to do this with a huge list, and duplicating the list seemed expensive, especially since in my case the number of deletions would be few c (Ep. First of all you'll need to replace foreach loop with while loop. Why do keywords have to be reserved words? As an example, I will create a random list of tuples somelist = [(1,2,3), (4,5,6), (3,6,6), (7,8,9), (15,0,0), (10,11,12)]. "The for statement", https://docs.python.org/2/reference/compound_stmts.html#for. For practical purposes, you can think of it as creating a reversed copy of its argument. This part of the docs says once again that you have to make a copy, and gives an actual removal example: Note: There is a subtlety when the sequence is being modified by the loop (this can only occur for mutable sequences, i.e. I will try to address that here: List comprehensions provide a way to generate a new list but these approaches tend to look at each element in isolation rather than the current state of the list as a whole. ChatGPT) is banned, Testing native, sponsored banner ads on Stack Overflow (starting July 6), Python: Removing list element while iterating over list. with list.copy() because I find it quite direct and intuitive. The lambda function we passed to filter gets called with each element of the So we modify your code and run it again: This code runs without any error, but let's look at the list it outputs: Why is (1,-2) still in your list? use del with an index as mentioned at: https://stackoverflow.com/a/1207485/895245.
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