![]() That said, there is not a huge penalty with smaller list sizes, but when you scale up the penalty becomes tremendous. This simply means learning the built-in methods. Use the built-in methods unless you really do need to do something custom. Method 4: Reverse list with Custom/Manual indexingĪs the timing shows, creating your own methods of indexing is a bad idea. Test with both a raw iterator, and creating a list from the iterator. This creates a copy and does not affect the original object.Great if you are feeding it to a loop for better performance on large lists ![]() This creates a reverse index iterator, not a list.There is a reversed(indexed_object) function: Method 3: Reverse a list with the reversed(obj) iterator function When the step size is negative, it will start with the last item and index backward by that amount. Indexing allows one to use negative numbers, which count from the end of the object's index backwards (i.e. When leaving an option empty, it sets them to defaults of the first and last element of the object (reversed if the step size is negative). To exploit slicing to create a simple reversed list, use. The built-in index slicing method allows you to make a copy of part of any indexed object. Method 2: Reverse a list using slices obj We test the performance of this two ways - first just reversing a list in-place (changes the original list), and then copying the list and reversing it afterward to see if that is the fastest way to create a reversed copy compared to the other methods. Typically, you wouldn't make a function for this, but the timing script requires it. you can create a copy by using this function output. Note that the following will reverse the original variable that is given, even though it also returns the reversed list back. Run this directly on a list object, and the order of all items will be reversed: If the goal is just to reverse the order of the items in an existing list, without looping over them or getting a copy to work with, use the. Method 1: Reverse in place with obj.reverse() The results are shown in the last section for lists of length 2, 10, and 1000 items. It will time each method while running it 100,000 times. Put all the code snippets in this answer together to make a script that will run the different ways of reversing a list that are described below. They are also less prone to defects and more likely to handle edge and corner cases. C), have experts creating them, scrutiny, and optimization. This makes sense - they are written in a native language (i.e. For reversing, they are 2 to 8 times faster on short lists (10 items), and up to ~300+ times faster on long lists compared to a manually-created loop or generator. Best solution is using slices with a -1 step size: objectįrom a speed perspective, it is best to use the above built-in functions to reverse a list.Create a copy of the list, just in the reverse order (to preserve the original list).Best solution is reversed(object) which creates the iterator.Create an iterator of the reversed list (because you are going to feed it to a for-loop, a generator, etc.).Best solution is object.reverse() method.Reverse an existing list in-place (altering the original list variable).Which method is best depends on whether you need to: There are three different built-in ways to reverse a list. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |