I want to group students with similar scores with 5 points up/ down.

public class Students
{
    public string Name {get; set;}
    public int Marks {get; set;}
    public int GroupID {get; set;}
}

public static void Main()
{
    List<Students> students = new List<Students>();
    
    students.Add(new Students { Name = "Aakash", Marks=89, GroupID=0 });
    students.Add(new Students { Name = "Prakash", Marks=85, GroupID=0  });
    students.Add(new Students { Name = "Ramesh", Marks=40, GroupID=0  });
    students.Add(new Students { Name = "Neha", Marks=95, GroupID=0 });
    students.Add(new Students { Name = "Suresh", Marks=93, GroupID=0 });
}

Expected Output:

    GroupID 1:
    Aakash, Prakash
    
    Group 2:
    Ramesh
        
    GroupID 3:
    Neha, Suresh

Any help is appreciated. Thanks.

Update:

What happens when students with marks of 4, 8, 12, 16, 20 & 24?

Ans: They would be different groups like this- 4 & 8 in Group 1, 12 & 16 in Group 2 and 20 & 24 in Group 3.

CodePudding user response：

If you want to determine the range of marks for each group based on the highest mark in that group, you may write something like this:

var ordered = students.OrderByDescending(s => s.Marks).ToList();
int groupId = 0;
int nextIndex = 0;
while (nextIndex < ordered.Count)
{
    groupId  ;
    var firstInGroup = ordered[nextIndex];
    var group = ordered.Skip(nextIndex).
                        TakeWhile(s => firstInGroup.Marks - s.Marks <= 5).ToList();
    group.ForEach(s => s.GroupID = groupId);
    nextIndex  = group.Count;
}

To make this reusable and to allow grouping to happen in either direction, you can turn this into a helper method like so:

enum MarkGroupingOption { HighestToLowest, LowestToHighest }

static void SetGroupIds(List<Students> students, int marksThreshold, 
                        MarkGroupingOption groupingOption)
{
    var ordered = (groupingOption == MarkGroupingOption.HighestToLowest
        ? students.OrderByDescending(s => s.Marks).ToList()
        : students.OrderBy(s => s.Marks).ToList());

    int groupId = 0;
    int nextIndex = 0;
    while (nextIndex < ordered.Count)
    {
        groupId  ;
        var firstInGroup = ordered[nextIndex];
        var remaining = ordered.Skip(nextIndex);
        var group = (groupingOption == MarkGroupingOption.HighestToLowest
            ? remaining.TakeWhile(s => firstInGroup.Marks - s.Marks <= marksThreshold)
            : remaining.TakeWhile(s => s.Marks - firstInGroup.Marks <= marksThreshold)
            ).ToList();
        group.ForEach(s => s.GroupID = groupId);
        nextIndex  = group.Count;
    }
}

Usage:

SetGroupIds(students, 5, MarkGroupingOption.HighestToLowest);

SetGroupIds(students, 5, MarkGroupingOption.LowestToHighest);