In a query expression, theselect clause specifies the type of values that will be produced when the query is executed. The result is based on the evaluation of all the previous clauses and on any expressions in theselect clause itself. A query expression must terminate with either aselect clause or agroup clause.

The following example shows a simpleselect clause in a query expression.

class SelectSample1{    static void Main()    {        //Create the data source        List<int> Scores = [97, 92, 81, 60];        // Create the query.        IEnumerable<int> queryHighScores =            from score in Scores            where score > 80            select score;        // Execute the query.        foreach (int i in queryHighScores)        {            Console.Write(i + " ");        }    }}//Output: 97 92 81

The type of the sequence produced by theselect clause determines the type of the query variablequeryHighScores. In the simplest case, theselect clause just specifies the range variable. This causes the returned sequence to contain elements of the same type as the data source. For more information, seeType Relationships in LINQ Query Operations. However, theselect clause also provides a powerful mechanism for transforming (orprojecting) source data into new types. For more information, seeData Transformations with LINQ (C#).

Example

The following example shows all the different forms that aselect clause may take. In each query, note the relationship between theselect clause and the type of thequery variable (studentQuery1,studentQuery2, and so on).

class SelectSample2{    // Define some classes    public class Student    {        public required string First { get; init; }        public required string Last { get; init; }        public required int ID { get; init; }        public required List<int> Scores;        public ContactInfo? GetContactInfo(SelectSample2 app, int id)        {            ContactInfo? cInfo =                (from ci in app.contactList                where ci.ID == id                select ci)                .FirstOrDefault();            return cInfo;        }        public override string ToString() => $"{First} {Last}:{ID}";    }    public class ContactInfo    {        public required int ID { get; init; }        public required string Email { get; init; }        public required string Phone { get; init; }        public override string ToString() => $"{Email},{Phone}";    }    public class ScoreInfo    {        public double Average { get; init; }        public int ID { get; init; }    }    // The primary data source    List<Student> students =    [         new Student {First="Svetlana", Last="Omelchenko", ID=111, Scores= new List<int>() {97, 92, 81, 60}},         new Student {First="Claire", Last="O'Donnell", ID=112, Scores= new List<int>() {75, 84, 91, 39}},         new Student {First="Sven", Last="Mortensen", ID=113, Scores= new List<int>() {88, 94, 65, 91}},         new Student {First="Cesar", Last="Garcia", ID=114, Scores= new List<int>() {97, 89, 85, 82}},    ];    // Separate data source for contact info.    List<ContactInfo> contactList =    [        new ContactInfo {ID=111, Email="SvetlanO@Contoso.com", Phone="206-555-0108"},        new ContactInfo {ID=112, Email="ClaireO@Contoso.com", Phone="206-555-0298"},        new ContactInfo {ID=113, Email="SvenMort@Contoso.com", Phone="206-555-1130"},        new ContactInfo {ID=114, Email="CesarGar@Contoso.com", Phone="206-555-0521"}    ];    static void Main(string[] args)    {        SelectSample2 app = new SelectSample2();        // Produce a filtered sequence of unmodified Students.        IEnumerable<Student> studentQuery1 =            from student in app.students            where student.ID > 111            select student;        Console.WriteLine("Query1: select range_variable");        foreach (Student s in studentQuery1)        {            Console.WriteLine(s.ToString());        }        // Produce a filtered sequence of elements that contain        // only one property of each Student.        IEnumerable<String> studentQuery2 =            from student in app.students            where student.ID > 111            select student.Last;        Console.WriteLine("\r\n studentQuery2: select range_variable.Property");        foreach (string s in studentQuery2)        {            Console.WriteLine(s);        }        // Produce a filtered sequence of objects created by        // a method call on each Student.        IEnumerable<ContactInfo> studentQuery3 =            from student in app.students            where student.ID > 111            select student.GetContactInfo(app, student.ID);        Console.WriteLine("\r\n studentQuery3: select range_variable.Method");        foreach (ContactInfo ci in studentQuery3)        {            Console.WriteLine(ci.ToString());        }        // Produce a filtered sequence of ints from        // the internal array inside each Student.        IEnumerable<int> studentQuery4 =            from student in app.students            where student.ID > 111            select student.Scores[0];        Console.WriteLine("\r\n studentQuery4: select range_variable[index]");        foreach (int i in studentQuery4)        {            Console.WriteLine($"First score = {i}");        }        // Produce a filtered sequence of doubles        // that are the result of an expression.        IEnumerable<double> studentQuery5 =            from student in app.students            where student.ID > 111            select student.Scores[0] * 1.1;        Console.WriteLine("\r\n studentQuery5: select expression");        foreach (double d in studentQuery5)        {            Console.WriteLine($"Adjusted first score = {d}");        }        // Produce a filtered sequence of doubles that are        // the result of a method call.        IEnumerable<double> studentQuery6 =            from student in app.students            where student.ID > 111            select student.Scores.Average();        Console.WriteLine("\r\n studentQuery6: select expression2");        foreach (double d in studentQuery6)        {            Console.WriteLine($"Average = {d}");        }        // Produce a filtered sequence of anonymous types        // that contain only two properties from each Student.        var studentQuery7 =            from student in app.students            where student.ID > 111            select new { student.First, student.Last };        Console.WriteLine("\r\n studentQuery7: select new anonymous type");        foreach (var item in studentQuery7)        {            Console.WriteLine("{0}, {1}", item.Last, item.First);        }        // Produce a filtered sequence of named objects that contain        // a method return value and a property from each Student.        // Use named types if you need to pass the query variable        // across a method boundary.        IEnumerable<ScoreInfo> studentQuery8 =            from student in app.students            where student.ID > 111            select new ScoreInfo            {                Average = student.Scores.Average(),                ID = student.ID            };        Console.WriteLine("\r\n studentQuery8: select new named type");        foreach (ScoreInfo si in studentQuery8)        {            Console.WriteLine("ID = {0}, Average = {1}", si.ID, si.Average);        }        // Produce a filtered sequence of students who appear on a contact list        // and whose average is greater than 85.        IEnumerable<ContactInfo> studentQuery9 =            from student in app.students            where student.Scores.Average() > 85            join ci in app.contactList on student.ID equals ci.ID            select ci;        Console.WriteLine("\r\n studentQuery9: select result of join clause");        foreach (ContactInfo ci in studentQuery9)        {            Console.WriteLine("ID = {0}, Email = {1}", ci.ID, ci.Email);        }    }}/* Output    Query1: select range_variable    Claire O'Donnell:112    Sven Mortensen:113    Cesar Garcia:114    studentQuery2: select range_variable.Property    O'Donnell    Mortensen    Garcia    studentQuery3: select range_variable.Method    ClaireO@Contoso.com,206-555-0298    SvenMort@Contoso.com,206-555-1130    CesarGar@Contoso.com,206-555-0521    studentQuery4: select range_variable[index]    First score = 75    First score = 88    First score = 97    studentQuery5: select expression    Adjusted first score = 82.5    Adjusted first score = 96.8    Adjusted first score = 106.7    studentQuery6: select expression2    Average = 72.25    Average = 84.5    Average = 88.25    studentQuery7: select new anonymous type    O'Donnell, Claire    Mortensen, Sven    Garcia, Cesar    studentQuery8: select new named type    ID = 112, Average = 72.25    ID = 113, Average = 84.5    ID = 114, Average = 88.25    studentQuery9: select result of join clause    ID = 114, Email = CesarGar@Contoso.com*/

As shown instudentQuery8 in the previous example, sometimes you might want the elements of the returned sequence to contain only a subset of the properties of the source elements. By keeping the returned sequence as small as possible you can reduce the memory requirements and increase the speed of the execution of the query. You can accomplish this by creating an anonymous type in theselect clause and using an object initializer to initialize it with the appropriate properties from the source element. For an example of how to do this, seeObject and Collection Initializers.

Remarks

At compile time, theselect clause is translated to a method call to theSelect standard query operator.

See also

• Query Keywords (LINQ)
• from clause
• partial (Method) (C# Reference)
• Anonymous Types
• LINQ in C#