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Converting Data Types

Conversion methods change the type of input objects.

Conversion operations in LINQ queries are useful in a variety of applications. Following are some examples:

The following table lists the standard query operator methods that perform data-type conversions.

The conversion methods in this table whose names start with "As" change the static type of the source collection but do not enumerate it. The methods whose names start with "To" enumerate the source collection and put the items into the corresponding collection type.

Method Name

Description

C# Query Expression Syntax

Visual Basic Query Expression Syntax

More Information

AsEnumerable

Returns the input typed as IEnumerable(Of T).

Not applicable.

Not applicable.

Enumerable.AsEnumerable(Of TSource)

AsQueryable

Converts a (generic) IEnumerable to a (generic) IQueryable.

Not applicable.

Not applicable.

Queryable.AsQueryable

Cast

Casts the elements of a collection to a specified type.

Use an explicitly typed range variable. For example:

from string str in words

From … As …

Enumerable.Cast(Of TResult)

Queryable.Cast(Of TResult)

OfType

Filters values, depending on their ability to be cast to a specified type.

Not applicable.

Not applicable.

Enumerable.OfType(Of TResult)

Queryable.OfType(Of TResult)

ToArray

Converts a collection to an array. This method forces query execution.

Not applicable.

Not applicable.

Enumerable.ToArray(Of TSource)

ToDictionary

Puts elements into a Dictionary(Of TKey, TValue) based on a key selector function. This method forces query execution.

Not applicable.

Not applicable.

Enumerable.ToDictionary

ToList

Converts a collection to a List(Of T). This method forces query execution.

Not applicable.

Not applicable.

Enumerable.ToList(Of TSource)

ToLookup

Puts elements into a Lookup(Of TKey, TElement) (a one-to-many dictionary) based on a key selector function. This method forces query execution.

Not applicable.

Not applicable.

Enumerable.ToLookup

The following code example uses an explicitly-typed range variable in C# or the From As clause in Visual Basic to cast a type to a subtype before accessing a member that is available only on the subtype.

Class Plant
    Public Name As String 
End Class 

Class CarnivorousPlant
    Inherits Plant
    Public TrapType As String 
End Class 

Sub Cast()

    Dim plants() As Plant = { _
        New CarnivorousPlant With {.Name = "Venus Fly Trap", .TrapType = "Snap Trap"}, _
        New CarnivorousPlant With {.Name = "Pitcher Plant", .TrapType = "Pitfall Trap"}, _
        New CarnivorousPlant With {.Name = "Sundew", .TrapType = "Flypaper Trap"}, _
        New CarnivorousPlant With {.Name = "Waterwheel Plant", .TrapType = "Snap Trap"}}

    Dim query = From plant As CarnivorousPlant In plants _
                Where plant.TrapType = "Snap Trap" _
                Select plant

    Dim sb As New System.Text.StringBuilder()
    For Each plant In query
        sb.AppendLine(plant.Name)
    Next 

    ' Display the results.
    MsgBox(sb.ToString())

    ' This code produces the following output: 

    ' Venus Fly Trap 
    ' Waterwheel Plant 

End Sub

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