CODEWITHSUNDEEP
c#.netlinq
user1512559
user1512559

Reputation:

Ranking items in a list with LINQ

I am trying to figure out a way to rank items in a list, and hold the results in an object or another list. I know about the orderby method, but I don't exactly know how to go about creating a corresponding rank number for each item.

For example:

List<int> numbers = new List<int>();

numbers.Add(650);
numbers.Add(150);
numbers.Add(500);
numbers.Add(200);

and then store the results from either low to high or high to low here:

public class NumberRank
{
    public int Number {get; set;}
    public int Rank {get; set;}

    public NumberRank(int number)
    {
        Number = number;
        Rank = ????????;
    }
}

Any solutions through LINQ?

Upvotes: 8

Views: 15950

Answers (3)

smirkingman
smirkingman

Reputation: 6368

Function Rank(Of T As IComparable)(list As IEnumerable(Of T), item As T) As Integer
    Return list.Count(Function(x) x.CompareTo(item) < 0) + 1
End Function

Public Sub Main()
    Dim l = New Integer() {9, 1, 3, 8, 4, 6}
    Console.WriteLine("6 is the " & Rank(l,6) & "th element of ")
    Console.WriteLine([String].Join(" ", l))
End Sub

6 is the 4th element of
9 1 3 8 4 6

Or, in C# http://dotnetfiddle.net/3ZGeJ1

Upvotes: 1

Cyril Gandon
Cyril Gandon

Reputation: 17058

One of the overload of the Select extension method return the index:

Projects each element of a sequence into a new form by incorporating the element's index.

You can use it to make your rank:

public class NumberRank
{
    public int Number {get; set;}
    public int Rank {get; set;}

    public NumberRank(int number, int rank)
    {
        Number = number;
        Rank = rank;
    }
}

List<int> numbers = new List();

numbers.Add(650);
numbers.Add(150);
numbers.Add(500);
numbers.Add(200);

numbers.OrderBy(n => n)
       .Select((n, index) => new NumberRank(n, index));

Upvotes: 18

A Coder
A Coder

Reputation: 3046

This should do it:

public class NumberRank
{
   public int Number {get; set;}
   public int Rank {get; set;}

   public NumberRank(int number, int rank)
   {
      Number = number;
      Rank = rank;
   }
}

class Test
{
   static void Main()
   {
      List<int> numbers = new List<int>();

      numbers.Add(650);
      numbers.Add(150);
      numbers.Add(500);
      numbers.Add(200);

      List<NumberRank> numberRanks = numbers.OrderByDescending(n => n).Select((n, i) => new NumberRank(n, i + 1)).ToList();

      // check it worked
      foreach(NumberRank nr in numberRanks) Console.WriteLine("{0} : {1}", nr.Rank, nr.Number);
      Console.ReadKey();  
   }
}

To rank in ascending order (i.e. lowest number first), then just replace OrderByDescending by OrderBy.

Upvotes: 12

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