Not that I'm using objects as if they are sets the key is the data I'm interested in, and the value is only a boolean flag to tell if it's been "removed". array.slice (from, until) From: Slice the array starting from an element index Until: Slice the array until another element index For example, I want to slice the first three elements from the array above. Instead of writing complex loops and conditional. The slice ( ) method copies a given part of an array and returns that copied part as a new array. Since Array.splice() and Array.pop() tend to have pretty bad performance characteristics, I suggest replacing the () implementation with a simple overwrite-with-undefined, and updating all of our array iterations to test for undefined.Īlternatively, if elements are going to be created and deleted often, it might even be better to use objects, instead. One of the main benefits of using array methods is that they can help improve the performance of your code. Wrap Up You can use the splice method of arrays to remove, replace and add items to an array. The removedItems is an empty array as nothing is removed. Ok, now back to the issue with Array.splice() ) At start position 1, no items are removed, and the added values 1000, and 2000 are added to the array at that position. It also tells me that iterating an object with a for.in loop and "removing" object properties by setting its value to 0 is going to be much faster than iterating arrays that need elements removed in ALMOST ALL CASES. This tells me arrays have strange scoping problems in Chrome. Now looking closely at group 3, both perform very well ~135MM and ~107MM respectively. The performance for the local scope test is HORRIBLE! ~11MM vs ~149MM (and pop is pretty bad too, at only ~16MM) 100k list splice and shift win, they mutate list slice loose, it creates a copy of list 7.5x slower Comparing performance of: slice vs splice vs shift slice. Looking more closely at group 2, array-undefined is almost exactly the same as the global variation, except they access an array in different scopes. If not specified, splice () will only remove elements from the array. , itemN (optional) - The elements to add to the start index. deleteCount (optional) - The number of items to remove from start. But that doesn't immediately discount object as being slower overall! The splice () method takes in: start - The index from where the array is changed. Now in group 1, I have two numbers indicating the relative speed: array gives ~32MM, and object gives ~12MM, meaning object is over 2x slower. In my test on Chrome 27, global array-undefined was fasted for group 2, and object-zero was fasted for group three. The "winners" from groups 2 and 3 can then be compared directly.
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