How to Sort 2D Array in C#

Question

I've read lots of posts about sorting a 2D array but I still can't master it so I was wondering if anyone can offer me some advice...

I have an aray which lists letters and quantity (I'm doing a frequency anaysis on a piece of text). I've read this data into a rectangle array and need to order it by highest frequency first. Here's my code so far:

    //create 2D array to contain ascii code and quantities
    int[,] letterFrequency = new int[26, 2];

    //fill in 2D array with ascaii code and quantities
    while (asciiNo <= 90)
     {

       while ((encryptedText.Length - 1) > counter)
      {
                if (asciiNo == (int)encryptedText[index])
               {
                      letterCount++;
               }
                counter++;
                index++;
      }

    letterFrequency[(storeCount), (0)] = (char)(storeCount+66);
    letterFrequency[(storeCount), (1)] = letterCount;
    storeCount++;
    counter=0;
    index=0;
    letterCount = 0;
    asciiNo++;
    }

Solution 1

You are using a 2D array to represent 2 separate vectors - the symbols and the counts. Instead, use 2 separate arrays. Array.Sort has an overload that takes 2 arrays, and sorts on one array, but applies the changes to both, achieving what you want.

This would also allow you to use a char[] for the characters rather than int[]:

char[] symbols = ...
int[] counts = ...
...load the data...
Array.Sort(counts, symbols);
// all done!

At this point, the counts have been ordered, and the symbols will still match index-by-index with the count they relate to.

Solution 2

You can wrap letter-count pair in a struct and use linq methods to manipulate data:

struct LetterCount {
    public char Letter { get; set; }
    public int Count { get; set; }
}

Sorting by count will look like this:

List<LetterCount> counts = new List<LetterCount>();
//filling the counts
counts = counts.OrderBy(lc => lc.Count).ToList();

Solution 3

public static void Sort2DArray<T>(T[,] matrix)
{
    var numb = new T[matrix.GetLength(0) * matrix.GetLength(1)];

    int i = 0;
    foreach (var n in matrix)
    {
        numb[i] = n;
        i++;
    }
    Array.Sort(numb);

    int k = 0;
    for (i = 0; i < matrix.GetLength(0); i++)
    {
        for (int j = 0; j < matrix.GetLength(1); j++)
        {
            matrix[i, j] = numb[k];
            k++;
        }
    }
}

Comments

[Aidiakapi]

Better make use of a SortedDictionary<TKey, TValue> then. But your other solution is the best :P.

[Aidiakapi]

That's the same as using the generic KeyValuePair<TKey, TValue>, except you get to name it.

[Marc Gravell]

@Aidiakapi no; that sorts on the key; we want to sort on the value

[Dmitry Polyanitsa]

Yes, but naming gives more readability and making a struct now can prepare the code for new logic in the future.

[Aidiakapi]

Sorry, I meant to say SortedList<TKey, TValue> ;)

[Aidiakapi]

Imo it just clutters code, but like I say that's my opinion. Just like C++ with it's typedefs. If you have a zillion types that all refer to the same type. Then it only gets confusing. Once again, my opinion.

[Dmitry Polyanitsa]

In this case it's a matter of taste, I agree.