Select bottom N from Generic List

Question

I have a generic list of integer and it contains random numbers. How would I select the last n elements from the list using LINQ?

I know can use myList.GetRange(index, count) to get the last n elements from the list. Is there a way to do it in LINQ?

THanks

regards, Balan

In general, I would not use Linq instead of functionality built into a type because it may be less performant. Linq works on IEnumerable meaning that the whole list must be traversed. GetRange may be more optimal. — Maciej, Apr 02 '12 at 05:28
@Maciej I was under the impression that LINQ was transparently optimised when operating on `ICollection` and `IList`. Depending on the query, it does not necessarily mean that the entire list must be traversed. — Bradley Smith, Apr 02 '12 at 05:53
@Bradley: Yes, in some cases it is optimized, but not always. See http://stackoverflow.com/questions/6245172/why-isnt-skip-in-linq-to-objects-optimized — Maciej, Apr 02 '12 at 11:13

ZeNo · Accepted Answer · 2012-04-02T05:29:06.563

10

var count = myList.Count;

myList.Skip(count-n)

Update:

removed redundant Take.

edited Apr 02 '12 at 05:29

answered Apr 02 '12 at 05:21

ZeNo

score 5 · Answer 2 · answered Apr 02 '12 at 05:16

5

You could use myList.Reverse().Take(n) to achieve what you want.

answered Apr 02 '12 at 05:16

Bradley Smith

6

You'd need an additional call to `Reverse` - `myList.Reverse().Take(n).Reverse()` - to return the elements in the same order as they are stored in the original list. – Lance U. Matthews Apr 02 '12 at 05:18
@BACON Good point, though order may not be important if the list contains only random numbers. – Bradley Smith Apr 02 '12 at 05:20

score 2 · Answer 3 · answered Apr 02 '12 at 05:13

2

Use skip:

myList.Skip(index).ToArray()

answered Apr 02 '12 at 05:13

McGarnagle

3 Answers3