How to check two IEnumerables whether they have same count without running through them individually. Means I do not want to do this Count() == Count().
I would like to find a way to do that in one pass. Any ideas?
Asked
Active
Viewed 242 times
1
-
Use IList or ICollection I think. – Jon Egerton Feb 17 '15 at 09:44
-
You can't. Enumerables might not even have a finite count. – Dirk Feb 17 '15 at 09:44
-
You can't do it unless you cast them to a type that has a Count property which allows you to get count without iterating all items. – Selman Genç Feb 17 '15 at 09:44
-
IEnumerable might not have a fixed count at any given time, depending on how it is being used. – Jon Egerton Feb 17 '15 at 09:44
1 Answers
3
This is not possible. Whatever approach you choose, you will have to run through both sequences.
The most straightforward way is to use the Count() method, where would be an O(1) if both sequences are List. In this case, the Count() fails to get the value of list's property called Count.
Christos
- 53,228
- 8
- 76
- 108
-
Using `Count()` will take time proportional to the longer collection; better is to check whether either or both collections implement either `ICollection` or `ICollection
`. If both do, compare their counts. If one does, read its count and try enumerating that N+1 items of the other. If the second collection ended after N, they match; if it ends sooner or doesn't end after N, they don't. If neither implements a counting interface, iterate them both *simultaneously*, and stop as soon as one reaches the end. – supercat Feb 19 '15 at 19:23