Question

Suppose I have one list:

IList<int> originalList = new List<int>(); originalList.add(1); originalList.add(5); originalList.add(10); 

And another list…

IList<int> newList = new List<int>(); newList.add(1); newList.add(5); newList.add(7);   newList.add(11); 

How can I update originalList so that:

1. If the int appears in newList, keep
2. If the int does not appear in newList, remove
3. Add any ints from newList into originalList that aren’t there already

Thus – making the contents of originalList:

{ 1, 5, 7, 11 } 

The reason I’m asking is because I have an object with a collection of children. When the user updates this collection, instead of just deleting all children, then inserting their selections, I think it would be more efficient if I just acted on the children that were added or removed, rather than tearing down the whole collection, and inserting the newList children as if they are all new.

EDIT – Sorry – I wrote a horrible title… I should have written ‘least amount of code’ instead of ‘efficient’. I think that threw off alot of the answers I’ve gotten. They are all great… thank you!

Answer 1

Sorry, wrote my first response before I saw your last paragraph.

for(int i = originalList.length-1; i >=0; --i) {      if (!newList.Contains(originalList[i])             originalList.RemoveAt(i); }  foreach(int n in newList) {      if (!originaList.Contains(n))            originalList.Add(n); }