Conversion methods in LINQ (Series)

In this post we are going to discuss on how we can convert IEnumerable type to different type (It can be either a List or Dictionary or Array). As we discussed in all our previous post of LINQ series, LINQ query either returns anonymous type(In the case of Select clause while using projections) or it returns type of IEnumerable or IQueryable. But sometime we require our IEnumerable data to be converted to other types like List or Dictionary or Array. In order to do, we have some extension methods, which will convert the IEnumerable type to the before said types. Let’s actually see them in action.

Converting IEnumerable Type to List

In order to convert IEnumerable type to List, use ToList() extension method available. Let’s take our same example which we have been dealing with this series so far.

//Create some students
List students = new List()
{
new Student { StudID = 101, Name= "Karthik", Class = "10th", Subjects = new List { "C#", "ADO.Net", "EF"}},
new Student { StudID = 108, Name= "Karthik", Class = "10th", Subjects = new List { "C#", "ADO.Net", "EF"}},
new Student { StudID = 104, Name = "Ram", Class = "11th", Subjects= new List{ ".Net", "C#", "SQL", "EF"}},
new Student { StudID = 103, Name = "John", Class = "9th", Subjects= new List{ ".Net", "MVC"}},
new Student { StudID = 106, Name = "Bill", Class = "9th", Subjects= new List{ "EF", "MVC"}},
};

Let’s query all the students and order them to descending by StudID and convert it to List

//Convert to List
List<Student,> studs  = (from student in students
                     orderby student.StudID descending
                     select student).ToList();

foreach (Student item in studs)
    Console.WriteLine(item.StudID + "\t" + item.Name);

As you can see above, we are using ToList() method to convert IEnumerable type to List. Then return value is of type List<Student>. We can then iterate all the elements using foreach loop as shown above.

Converting IEnumerable Type to Dictionary

Similar to List, we can convert IEnumerable type to Dictionary using ToDictionary() method as shown below

//Convert to Dictionary
Dictionary<int, string> studDict = (from student in students
                                    orderby student.StudID descending
                                    select student).ToDictionary(x => x.StudID, y => y.Name);

foreach (KeyValuePair<int, string> item in studDict)
    Console.WriteLine(item.Key + "\t" + item.Value);

Since Dictionary collection has Key and Value pair, we need to specify the key and value in ToDictionary method, here I have assigned the key as StudID and value as Name. I have iterated the Dictionary in foreach loop, note I have used KeyValuePair<int, string> since that’s the type of Dictionary and then got all the key and value out from the collection.

Output

The output of both the above code looks like one shown below

Converting IEnumerable Type to Array

Here is the code

//Convert to Array
Student[] studs = (from student in students
                    orderby student.StudID descending
                    select student).ToArray();

foreach (Student item in studs)
    Console.WriteLine(item.StudID + "\t" + item.Name);

Here is the complete code

public static void ConvertToDifferentTypeInLINQ()
{
    //Create some students
    List students = new List()
    {
        new Student { StudID = 101, Name= "Karthik", Class = "10th", Subjects = new List { "C#", "ADO.Net", "EF"}},
        new Student { StudID = 108, Name= "Karthik", Class = "10th", Subjects = new List { "C#", "ADO.Net", "EF"}},
        new Student { StudID = 104, Name = "Ram", Class = "11th", Subjects= new List{ ".Net", "C#", "SQL", "EF"}},
        new Student { StudID = 103, Name = "John", Class = "9th", Subjects= new List{ ".Net", "MVC"}},
        new Student { StudID = 106, Name = "Bill", Class = "9th", Subjects= new List{ "EF", "MVC"}},
    };


    //Convert to List
    List studs = (from student in students
                            orderby student.StudID descending
                            select student).ToList();

    foreach (Student item in studs)
        Console.WriteLine(item.StudID + "\t" + item.Name);

    //Convert to Dictionary
    Dictionary<int, string> studDict = (from student in students
                                        orderby student.StudID descending
                                        select student).ToDictionary(x => x.StudID, y => y.Name);

    foreach (KeyValuePair<int, string> item in studDict)
        Console.WriteLine(item.Key + "\t" + item.Value);

    //Convert to Array
    Student[] studsArray = (from student in students
                        orderby student.StudID descending
                        select student).ToArray();

    foreach (Student item in studsArray)
        Console.WriteLine(item.StudID + "\t" + item.Name);


}

These are the different types of conversion methods available in LINQ which convert IEnumerable type to different types. Please leave your comments and thanks for reading !!! Thanks, Karthik KK