using System;

using System.Collections.Generic;

using System.Runtime.CompilerServices;

public class Program

{

    public static void Main()

    {

        List<MyItem[]> MyItems = new List<MyItem[]>()

        {

            new MyItem[] { new MyItem("Item1") },

            new MyItem[] { new MyItem("Item1"), new MyItem("Item2") },

            new MyItem[] { new MyItem("Item3") },

            new MyItem[] { new MyItem("Item1"), new MyItem("Item3"), new MyItem("Item2") },

            new MyItem[] { new MyItem("Item3"), new MyItem("Item1") },

            new MyItem[] { new MyItem("Item2"), new MyItem("Item1") }

        };

        Dictionary<Tuple<string, string>, int> results = new Dictionary<Tuple<string, string>, int>();      

        foreach (MyItem[] arr in MyItems)

        {

            // Iterate through the items in the array. Then, iterate through the items after that item in the array to get all combinations.

            for (int i = 0; i < arr.Length; i++)

            {

                string s1 = arr[i].ItemName;

                for (int j = i + 1; j < arr.Length; j++)

                {

                    string s2 = arr[j].ItemName;

                    // Order the Tuple so that (Item1, Item2) is the same as (Item2, Item1).                    

                    Tuple<string, string> t = new Tuple<string, string>(s1, s2);

                    if (string.Compare(s1, s2) > 0)

                    {

                        t = new Tuple<string, string>(s2, s1);  

                    }

                    if (results.ContainsKey(t))

                    {

                            results[t]++;

                    }

                    else

                    {

                        results[t] = 1;

                    }

                }

            }

        }

        // And here are your results.

        foreach (var v in results)

        {

            Console.WriteLine(v.Key.ToString() + " = " + v.Value.ToString());

        }

    }

}

​

public class MyItem

{

    public string ItemName { get; set; }

    public MyItem(string ItemName)

    {

        this.ItemName = ItemName;   

    }

}