LongCount (LINQ)

Enumerable.LongCount is extension method from System.Linq namespace. It counts number of items in collection just like Enumerable.Count method, but the result type is long (Int64) instead of int (Int32).

Use this method only if there is possibility that number of items in the IEnumerable collection is greater than Int32.MaxValue (2,147,483,647). Otherwise use Enumerable.Count because it is optimized for collections which implements ICollection (lists, arrays, dictionaries). See LongCount Implementation bellow.

LongCount Examples

Counts number of items in the IEnumerable collection.

IEnumerable<string> items = new List<string> { "A", "B", "C" }; long count = items.LongCount(); // count: 3

Returns 0 if there is no item in the collection.

IEnumerable<string> items = new List<string> { }; long count = items.LongCount(); // count: 0

LongCount with Predicate

Counts number of items which match specified predicate.

IEnumerable<int> items = new List<int> { 8, 3, 2 }; // these two lines do the same long count = items.Where(x => x < 5).LongCount(); // count: 2 long count = items.LongCount(x => x < 5); // count: 2

LongCount with Query Syntax

LINQ query expression to count number of all items in the collection.

IEnumerable<int> items = new List<int> { 8, 3, 2 }; long count = (from x in items select x).LongCount(); // count: 3

LINQ query expression to count number of items which match specified predicate.

IEnumerable<int> items = new List<int> { 8, 3, 2 }; long count = (from x in items where x < 5 select x).LongCount(); // count: 2

LongCount Implementation

This is .NET Framework implementation of Enumerable.LongCount method. Note that implementation of LongCount is more performance-intensive in some cases than implementation of Enumerable.Count. It's because Enumerable.Count implementation first checks whether the IEnumerable can be cast to ICollection (which is List, array [], Dictionary, HashSet). If so, it simply returns value of its Count property (of type int). LongCount implementation doesn't do the optimization and always simply counts the items.

public static long LongCount<TSource>(this IEnumerable<TSource> source) { if (source == null) throw Error.ArgumentNull("source"); long count = 0; using (IEnumerator<TSource> e = source.GetEnumerator()) { checked { while (e.MoveNext()) count++; } } return count; }

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C# LINQ Aggregation Methods

LongCount (LINQ)

LongCount Examples

LongCount with Predicate

LongCount with Query Syntax

LongCount Implementation

See also