{TOC}
| Namespace: | System.Linq |
| Assembly: | System.Core.dll |
| Extends: | IEnumerable<T> |
Back to
Standard Query Operator IndexEditIntroduction
The Count operator counts the number of elements in a sequence, or the numer of elements that pass a predicate function.
EditMethod Signatures
// 1 - Return the count of elements in source.
public static int Count<TSource>(
this IEnumerable<TSource> source)
// 2 - Return the count of elements in sequence that pass the predicate.
public static int Count<TSource>(
this IEnumerable<TSource> source,
Func<TSource, bool> predicate)EditExceptions
Throws an ArgumentNullException if
source or
predicate is null.
EditPseudocode
Overload 1
If
source is null, throw ArgumentNullException.
If source is of type
ICollection<TSource>.
Return source.Count; property. This ia a performance enhancement.
Else, we need to enumerate the collection.
Initialize count result as 0.
Iterate over the source sequence.
count result = previous count result value + 1.
Return the count result value.
Overload 2
If
source is null, throw ArgumentNullException.
If
predicate is null, throw an ArgumentNullException.
Initialize count result as 0.
Iterate the source sequence
If predicate (current element) returns true, count result = previous count result value + 1.
Return the count result value.
EditLoop Count
Overload 1
If the source is of type ICollection, then the Count property of the original source sequence is returned, otherwise the entire sequence is enumerated and counted.
Overload 2
1. The entire sequence is iterated once and predicate evaluated once for every source sequence item.
EditCode Samples
==VB Counts how many items are in your Favorites folder==
Public Sub Linq()
Dim FavPath As String = Environment.GetFolderPath(Environment.SpecialFolder.Favorites)
Dim FavSize = (From f In New DirectoryInfo(FavPath).GetFiles() _
Select f).Count()
Console.WriteLine("There are {0} files in your Favorites folder.", FavSize)
End Sub
Result may vary,
There are 5 files in your Favorites folder.