How to sort a List of integer arrays of varying size?

Question

I've done some extensive searching for this so if this is a duplicate please slaughter me :D

I have a List of byte arrays (List) where the arrays are of varying length. I need to sort the list by the array lengths in ascending order then by the bytes in the array (please see example).

Example:

I want to go from:

{0,1,2}
{0,4}
{0,3,2}
{0,1,3}
{0,2,4,6,1}
{0,1,1}
{0,3,4,5}

to:

{0,4}
{0,1,1}
{0,1,2}
{0,1,3}
{0,3,2}
{0,3,4,5}
{0,2,4,6,1}

It's essentially alphabetical order but with a set of numbers instead of characters (arguably the same thing), any ideas?

Write a custom comparer.

Erti-Chris Eelmaa
– Erti-Chris Eelmaa

2015-02-14 17:12:06 +00:00
Commented Feb 14, 2015 at 17:12 — Erti-Chris Eelmaa
– Erti-Chris Eelmaa, Commented Feb 14, 2015 at 17:12

willeM_ Van Onsem · Accepted Answer · 2015-02-14 17:19:31Z

The only thing you need to do is implement a IComparer<T> interface and provide that to the sorting algorithm. In this case the algorithm looks like:

public ByteArrayComparer : IComparer<byte[]> {

    public int Compare (byte[] ba, byte[] bb) {
        int n = ba.Length;  //fetch the length of the first array
        int ci = n.CompareTo(bb.Length); //compare to the second
        if(ci != 0) { //if not equal return the compare result
            return ci;
        } else { //else elementwise comparer
            for(int i = 0; i < n; i++) {
                if(ba[i] != bb[i]) { //if not equal element, return compare result
                    return ba[i].CompareTo(bb[i]);
                }
            }
            return 0; //if all equal, return 0
        }
    }

}

Next you can use the List<T>.Sort method:

List<byte[]> data = new List<byte[]>();
//add arrays to data
data.Sort(new ByteArrayComparer());
//data is now sorted

The sorting algorithm requires that the comparator is valid, a comparator is valid if it satisfies the three constraints on an ordering relation:

Reflexivity: if an elements is compared with itself, return 0;
Anti-symmetric: If x is smaller than y (return something less than 0), then y is greater than x (something greater than 0);
Transitive: if x is smaller than y and y is smaller than z, then x is smaller than z.

If the comparer doesn't satisfy that relation, the sorting algorithm will fail to sort correctly, simply because your order makes no sense.

Kavindu Dodanduwa · Accepted Answer · 2015-02-14 17:55:04Z

2

Why not simply use LINQ

MyList = MyList.OrderBy(arr=>arr.Length).ThenBy(arr =>arr.Sum()).ToList();

A working example :

   List<int[]> a = new List<int[]>();

   int[] t1 = { 0, 4 };
   int[] t2 = { 0, 1, 2 };
   int[] t3 = { 0, 1, 3 };
   int[] t4 = { 0, 2, 4, 6, 1 };
   int[] t5 = { 0, 1, 1 };
   int[] t6 = { 0, 3, 4, 5 };

   a.Add(t1);
   a.Add(t2);
   a.Add(t3);
   a.Add(t4);
   a.Add(t5);
   a.Add(t6);

   a = a.OrderBy(arr=>arr.Length).ThenBy(arr =>arr.Sum()).ToList();

    foreach (int[] item in a)
    {
        foreach (int item2 in item)
        {
             Console.Write(" "+item2);
      }
      Console.WriteLine();
   }

Sample output :

And as pointed out this could fail in scenarios like {3 4 5} , {4 5 3}

edited Feb 14, 2015 at 17:55

answered Feb 14, 2015 at 17:15

Kavindu Dodanduwa

13.2k4 gold badges38 silver badges49 bronze badges

2 Comments

willeM_ Van Onsem Over a year ago

I didn't dv, but I think it's still incorrect. I think the OP wants to sort lexicographically. So that {1,200} is less than {3,5} because the first element is smaller. If not look to the second and so on...

The One Over a year ago

What's first? {0,3,4,5} or {0,3,5,4} ?

Collectives™ on Stack Overflow

How to sort a List of integer arrays of varying size?

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related