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{TOC}

Back to Standard Query Operator Index


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Introduction

The Count operator counts the number of elements in a sequence, or the numer of elements that pass a predicate function.

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Method 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)

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Exceptions

Throws an ArgumentNullException if source or predicate is null.

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Pseudocode

Overload 1
If source is null, throw ArgumentNullException.
If source is of type ICollection<TSource>.
Else, we need to enumerate the collection.

Overload 2
If source is null, throw ArgumentNullException.
If predicate is null, throw an ArgumentNullException.
Initialize count result as 0.
Iterate the source sequence
Return the count result value.

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Loop 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.


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Code 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.

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