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LINQ to Objects

Aggregation

Aggregate, Average, Count, LongCount, Max, Min, Sum

      Aggregate (simple)       Aggregate (seed)       Average       Count       LongCount       Max       Min       Sum

Conversion

AsEnumerable, Cast, OfType, ToArray, ToDictionary, ToList, ToLookup

      AsEnumerable       Cast       OfType       ToArray       ToDictionary (simple)       ToDictionary (conditional)       ToList       ToLookup

Element

ElementAt, ElementAtOrDefault, First, FirstOrDefault, Last, LastOrDefault, Single, SingleOrDefault

      ElementAt       ElementAtOrDefault       First (simple)       First (conditional)       FirstOrDefault       Last       LastOrDefault (simple)       LastOrDefault (conditional)       Single       SingleOrDefault

Generation

DefaultIfEmpty, Empty, Range, Repeat

      DefaultIfEmpty (simple)       DefaultIfEmpty (default value)       Empty       Range       Repeat

Grouping

GroupBy

      GroupBy

Join

GroupJoin, Join

      GroupJoin (left outer join)       Join (inner join)

Ordering

OrderBy, OrderByDescending, Reverse, ThenBy, ThenByDescending

      OrderBy (simple - numbers)       OrderBy (simple - dates)       OrderBy (simple - objects)       OrderByDescending       Reverse       ThenBy       ThenByDescending

Other

Concat, SequenceEqual, Zip

      Concat (simple - numbers)       Concat (simple - strings)       SequenceEqual       Zip

Partitioning

Skip, SkipWhile, Take, TakeWhile

      Skip       SkipWhile       Take       TakeWhile

Projection

Select, SelectMany

      Select (simple)       Select (anonymous type)       Select (indexed)       SelectMany (cross join)

Quantifiers

All, Any, Contains

      All       Any       Contains

Restriction

Where

      Where (simple - numbers)       Where (simple - objects)       Where (indexed)

Set

Distinct, Except, Intersect, Union

      Distinct       Except       Intersect       Union
  Close

Count

Lambda Query

Count: Returns the number of elements in a collection.

Count: Returns the number of elements in a collection.

This Lambda Expression sample counts names in array.

This Lambda Expression sample counts names in array.

  • C#
  • VB.Net
  • F#
// A Query Expression cannot be constructed for Count() in C#.
// Consider using a Lambda Expression instead.
Private Shared Sub Sample_Count_Linq()
    Dim names As String() = {"Peter", "John", "Kathlyn", "Allen", "Tim"}

    Dim result = Aggregate n In names Into Count()

    Debug.WriteLine("Counting names gives:")
    Debug.WriteLine(result)
End Sub
Output:
Counting names gives:
5
let Sample_Count_Linq() =
    let names = [|"Peter"; "John"; "Kathlyn"; "Allen"; "Tim"|]

    let result = query {
        for n in names do
        count
    }

    Debug.WriteLine(sprintf "Counting names gives:")
    Debug.WriteLine(sprintf "%d" result)
Output:
Counting names gives:
5
  • C#
  • VB.Net
  • F#
static void Sample_Count_Lambda()
{
    string[] names = { "Peter", "John", "Kathlyn", "Allen", "Tim" };

    var result = names.Count();

    Debug.WriteLine("Counting names gives:");
    Debug.WriteLine(result);
}
Output:
Counting names gives:
5
Private Shared Sub Sample_Count_Lambda()
    Dim names As String() = {"Peter", "John", "Kathlyn", "Allen", "Tim"}

    Dim result = names.Count()

    Debug.WriteLine("Counting names gives:")
    Debug.WriteLine(result)
End Sub
Output:
Counting names gives:
5
let Sample_Count_Lambda() =
    let names = [|"Peter"; "John"; "Kathlyn"; "Allen"; "Tim"|]

    let result = names.Count()

    Debug.WriteLine(sprintf "Counting names gives:")
    Debug.WriteLine(sprintf "%d" result)
Output:
Counting names gives:
5

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