using System;

using System.Collections.Generic;

using System.Linq;

​

// SO Answer: https://stackoverflow.com/questions/78547351#78547669

​

public class DataItem {

    public string Metal { get; set; }

    public string value { get; set; }

}

public class Program

{

    public static void Main()

    {

        var data = new List<DataItem> {

            new DataItem { Metal = "silver",     value = "5" },

            new DataItem { Metal = "silver_ref", value = "Y" },

            new DataItem { Metal = "gold",       value = "2" },

            new DataItem { Metal = "gold_ref",   value = "N" },

            new DataItem { Metal = "iron",       value = "N" },

            new DataItem { Metal = "iron_ref",   value = "N" }

        };

​

        var query =

            from d1 in data

            join d2 in data on (d1.Metal + "_ref") equals d2.Metal

            where d1.value != "N" && d2.value == "Y"

            select d1;

        foreach (var item in query)

        {

            Console.WriteLine($"DataItem{{ Metal: {item.Metal}, value: {item.value} }}");

        }

    }

}