How to sort a list of lists in C#

Basically Sort() method of List<T> is used to sort the elements in a list but we need to sort a list of list elements.

Here is an example, we have a list of routes collection, and these should be sorted by distance.

Listint>> forwards = new Listint>> {

                new List<int>{1, 3000},  new List<int>{2, 5000},  new List<int>{3, 4000}, new List<int>{4, 10000}

            };

If we try to sort this list by using simply use the Sort() method of List<T> Type

forwards.Sort();

It throws below System.InvalidOperationException: 'Failed to compare two elements in the array.'

System.InvalidOperationException: 'Failed to compare two elements in the array.'

System.InvalidOperationException

  HResult=0x80131509

  Message=Failed to compare two elements in the array.

  Source=mscorlib

  StackTrace:

   at System.Collections.Generic.ArraySortHelper`1.Sort(T[] keys, Int32 index, Int32 length, IComparer`1 comparer)

   at System.Array.Sort[T](T[] array, Int32 index, Int32 length, IComparer`1 comparer)

   at System.Collections.Generic.List`1.Sort(Int32 index, Int32 count, IComparer`1 comparer)

   at System.Collections.Generic.List`1.Sort()

   at Sample.JobT.Main() in C:\Users\rtiwari\source\repos\PDFSharp_Merge\Sample\Program.cs:line 238

Inner Exception 1:

ArgumentException: At least one object must implement IComparable.

In this scenario, we need to define Own IComparer Interface implemented class

  

  class Comparer : IComparer<int>>

        {

            public int Compare(List<int> x, List<int> y)

            {

                if (x == null || y == null)

                {

                    return 0;

                }

                // "CompareTo()" method

                return x[1].CompareTo(y[1]);

            }

        }

  

Now the Sort() method is used to sort the elements in the entire List using the specified comparer – Comparer

forwards.Sort(new Comparer());

Here is a completed example

public static void Main()

        {

            List<List<int>> forwards = new List<List<int>> {

                new List<int>{1, 3000},  new List<int>{2, 5000},  new List<int>{3, 4000}, new List<int>{4, 10000}

            };

            foreach (var item in forwards)

            {

                string t = $"[{item[0]}, {item[1]}], ";

                Console.Write(t);

            }

            Console.WriteLine();

            Console.WriteLine("After Sorting");

            forwards.Sort(new Comparer());

            foreach (var item in forwards)

            {

                string t = $"[{item[0]}, {item[1]}], ";

                Console.Write(t);

            }

  }

Console Output: 

Here is a list of the collections of routes sorted by distance.