I have a list of items and I need to loop through it so that every n (eg. 3) items are first collected and then processed at once at the n'th item.
I'm doing the following:
List<MyObject> smallList = new List<MyObject>(); for (int i = 0; i < largeList.Count; i++) { smallList.Add(largeList[i]); if (i % 3 == 0 || i >= largeList.Count - 3) { //Do somehting with those n items... } smallList.Clear(); } Is there a better way to do the above?
You can also do this with LINQ:
var largeList = new List<int>(new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }); for (int i = 0; i < largeList.Count; i += 3) { var items = largeList.Skip(i).Take(3).ToList(); // do stuff with your 3 (or less items) } 
i=0, otherwise you miss the first three.
List implements the Skip method in a constant time returning some lazy iterator.You can do it with LINQ.
First, "attach" an index to each item:
var indexedItems = largeList.Select((item, index) => new {index, item}); Now group them by their index, while selecting the collection (IEnumerable) of items for each group member:
var groupedItems = indexedItems.GroupBy(indexedItem => indexedItem.index / 3, indexedItem => indexedItem.item, (key, items) => items); Now process each group
foreach(var items in groupedItems) { // and optionally, .ToList() to have a List<T> instead of IEnumerable<T> var itemsList = items.ToList(); } And altogether...:
var indexedItems = largeList.Select((item, index) => new {index, item}); var groupedItems = indexedItems.GroupBy(indexedItem => indexedItem.index / 3, indexedItem => indexedItem.item, (key, items) => items); foreach(var items in groupedItems) { // Use the items... } I suggest using nested loops. Not as pretty as LinQ, but certainly faster.
const int n = 3; var small = new List(); for(var i=0; i<large.Count; i+=n) { small.Clear(); for(var j=i; j < n && j<large.Count; j++) small.Add(large[j]); // Do stuff with small } However quite similar to what you have now. I think it doesn't get much butter than what you have.
you can use this code:
var MyObjectList = new List<MyObject>(); MyObjectList.Where(a => MyObjectList.IndexOf(a) % 3 == 0).ToList().ForEach(a => { // do your things! }); 