Question

I have some code that filters through a collection of sorted objects according to a filter value. For instance, I want to find the objects where Name=="searchquery". Then I want to take the top X values from that collection.

My questions:

• My collection is a List<T>. Does this collection guarantee the sort order?

• If so, is there a built-in way to find the the top X objects that satisfy the condition? I’m looking for something like

  collection.FindAll(o=>o.Name=="searchquery",100);
  

  That would give me the top 100 objects that satisfy the condition. The reason is performance, once I’ve found my 100 objects, I don’t want to keep checking the entire collection.

• If i write:

  collection.FindAll(o=>o.Name=="searchquery").Take(100);
  

  will the runtime be intelligent enough to stop checking once it hits 100?

I can of course implement this myself, but if there is a built-in way (like a LInQ method) I’d prefer to use it.

Answer 1

collection.Where(o=>o.Name=="searchquery").Take(100)

The order should be in the same order as the original list, and it will stop checking once it takes 100 elements (Where returns an enumeration which is only evaluated as you take elements). From the documentation:

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

If you need a different sort order, you will have to specify it (this of course means you have no choice but to examine all elements though).