Does LINQ Where clause honor order?

Question

When I use a LINQ Where clause, does the returned list of items honor the order they were in the original list?

Answer 1

It depends on how the collection being queried has its GetEnumerator is implemented. If GetEnumerator iterates through the collection in the order added, then it will honor order.

UPDATE:

Here's an example that I put together with LINQPad:

var items = new List<int>() { 1,2,3,4,5 };
items.Insert(3, 100);

(from i in items
 where i > 2
 select i).Dump();

RESULT:

3 
100
4
5

So, the Where clause honors the order of the items in the list since List's GetEnumerator starts at the first item in the list and proceeds through the end.

Answer 2

Where processes items in the order IEnumerable<T> gives. If you query an implementation of IEnumerable<T> thats keeps the order in which they are inserted (such as List<T>), then you keep the order. If you query a HashTable<T> for example, order is not guaranteed.