The best way to get a count of IEnumerable

Question

Whats the best/easiest way to obtain a count of items within an IEnumerable collection without enumerating over all of the items in the collection?

Possible with LIN

Answer 1

An IEnumerable will have to iterate through every item. to get the full count. If you just need to check if there is one or more items in an IEnumerable a more efficient method is to check if there are any. Any() only check to see there is a value and does not loop through everything.

IEnumerable myStrings = new List(){"one","two", "three"};

bool hasValues = myStrings.Any();

Answer 2

Not possible with LINQ, as calling .Count(...) does enumerate the collection. If you're running into the problem where you can't iterate through a collection twice, try this:

List<MyTableItem> myList = dataContext.MyTable.ToList();
int myTableCount = myList.Count;

foreach (MyTableItem in myList)
{
   ...
}

Answer 3

Use this.

IEnumerable list =..........;

list.OfType<T>().Count()

it will return the count.

Answer 4

You will have to enumerate to get a count. Other constructs like the List keep a running count.

Answer 5

In any case, you have to loop through it. Linq offers the Count method:

var result = myenum.Count();