CODEWITHSUNDEEP
c#linqgrouping
Pankaj
Pankaj

Reputation: 2744

List order by another contained list

I have a list of Objects and one of the item is another list. How can I Group them based on the inner list. Here is an example of what I wish to do. 

class Student
{
    public string Name;
    public int Age;
    public List<GroupInfo> GroupList; // This is the inner list
}

class GroupInfo
{
    public string GroupName;
    public int GroupId;
}

static void Main() 
{
   GroupInfo firstGroup = new GroupInfo
   {
      GroupId = 1,
      GroupName = "First group"
   };

   GroupInfo secondGroup = new GroupInfo
   {
       GroupId = 2,
       GroupName = "Second group"
    };

    GroupInfo thirdGroup = new GroupInfo
    {
       GroupId = 3,
       GroupName = "Third group"
    };

    GroupInfo fourthGroup = new GroupInfo
    {
       GroupId = 4,
       GroupName = "Fourth group"
    };

    List<Student> studentList = new List<Student>();

    Student firstStudent = new Student();
    firstStudent.Name = "Name1";
    firstStudent.Age = 15;
    firstStudent.GroupList = new List<GroupInfo>();
    firstStudent.GroupList.Add(firstGroup);
    firstStudent.GroupList.Add(secondGroup);
    studentList.Add(firstStudent);

    Student secondStudent = new Student();
    secondStudent.Name = "Name2";
    secondStudent.Age = 17;
    secondStudent.GroupList = new List<GroupInfo>();
    secondStudent.GroupList.Add(firstGroup);
    secondStudent.GroupList.Add(thirdGroup);
    studentList.Add(secondStudent);

    Student thirdStudent = new Student();
    thirdStudent.Name = "Name3";
    thirdStudent.Age = 18;
    thirdStudent.GroupList = new List<GroupInfo>();
    thirdStudent.GroupList.Add(secondGroup);
    thirdStudent.GroupList.Add(thirdGroup);
    thirdStudent.GroupList.Add(fourthGroup);
    studentList.Add(thirdStudent);

    List<GroupInfo> groupInfoList = new List<GroupInfo>();
   // Now What I want is to get a group List Where...
    foreach (var student in studentList)
    {
        // ...First Group Should contains firstStudent and secondStudent
        // Second group Should firstStudent & thirdStudent
        // Third group Should contains secondStudent & thirdStuden
        // Fourth Group Should contains only thirdStudent
      }
    }

One way is to iterate on the whole List and populate the GroupInfo List. Just wondering is there any other way to do this task.

Upvotes: 1

Views: 98

Answers (1)

Rahul Singh
Rahul Singh

Reputation: 21795

You can do this with SelectMany like this:-

var result = studentList.SelectMany(x => x.GroupList, 
                                      (studentObj, groups) => new { studentObj, groups })
                        .GroupBy(x => new { x.groups.GroupId, x.groups.GroupName })
                        .Select(x => new 
                               {
                                  GroupId = x.Key.GroupId,
                                  GroupName = x.Key.GroupName,
                                  Students = x.Select(z => z.studentObj).ToList()
                               });

Since your GroupInfo class only has two properties i.e. GroupId & GroupName, you won't be able to fetch the Students associated with it. This is the reason I am fetching anonymous type out of it.

I am getting following output with this query:-

enter image description here

Upvotes: 1

Related Questions