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++;
    }

Can you give an example (maybe smaller) of what a sorted 2D array looks like? Do you mean sorting each row separately, for example? — Marc Gravell, Jan 15 '12 at 00:00
Looks like you are getting some great feedback so I will bow out. I asked the C# question to ensure that you can take advantage of Linq Lambda Expressions. — Matt Cashatt, Jan 15 '12 at 00:03
The array will contain two columns - one for Character and one for frequency of that character. So in overview, it stores 26 different letters with it's associated frequency. — L1am22, Jan 15 '12 at 00:03
Sorry - to answer your sorting question, I want to sort the frequency column & have the associated letter with it. int[26,2] letterFrequency = {66, 17} etc...... Please note I'm storing the letter as it's ASCII code. — L1am22, Jan 15 '12 at 00:06

score 17 · Accepted Answer · answered Jan 15 '12 at 00:02

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.

score 4 · Answer 2 · answered Jan 15 '12 at 00:14

4

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();

answered Jan 15 '12 at 00:14

Dmitry Polyanitsa

1,083
9
18

That's the same as using the generic `KeyValuePair`, except you get to name it. – Aidiakapi Jan 15 '12 at 00:17
Yes, but naming gives more readability and making a struct now can prepare the code for new logic in the future. – Dmitry Polyanitsa Jan 15 '12 at 00:21
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. – Aidiakapi Jan 15 '12 at 00:27
In this case it's a matter of taste, I agree. – Dmitry Polyanitsa Jan 15 '12 at 00:33

score 1 · Answer 3 · answered Oct 15 '13 at 22:29

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++;
        }
    }
}

Aidiakapi · Answer 4 · 2012-01-15T00:24:25.700

In this case I'd choose to make use of KeyValuePair<TKey, TValue> and instead use something like this:

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

//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] = new KeyValuePair<char, int>((char)(storeCount+66), letterCount);
storeCount++;
counter=0;
index=0;
letterCount = 0;
asciiNo++;
}

Then use Array.Sort:

Array.Sort(letterFrequency, (i1, i2) => i2.Value.CompareTo(i1.Value));

score 0 · Answer 5 · answered Jan 15 '12 at 00:12

0

Alternative approach:

var counts = new Dictionary<char,int>();
foreach(char c in text) {
    int count;
    counts.TryGetValue(c, out count);
    counts[c] = count + 1;
}
var sorted = counts.OrderByDescending(kvp => kvp.Value).ToArray();
foreach(var pair in sorted) {
    Console.WriteLine("{0}: {1}", pair.Key, pair.Value);
}

(untested)

answered Jan 15 '12 at 00:12

Marc Gravell

1,026,079
266
2,566
2,900

Better make use of a `SortedDictionary` then. But your other solution is the best :P. – Aidiakapi Jan 15 '12 at 00:15
@Aidiakapi no; that sorts on the key; we want to sort on the value – Marc Gravell Jan 15 '12 at 00:18
Sorry, I meant to say `SortedList` ;) – Aidiakapi Jan 15 '12 at 00:23

Aidiakapi · Answer 6 · 2012-01-15T00:28:47.117

This'll sort a two dimension array, the bool specifies if it's sorted on the second dimension, but default it sorts on the first dimension.

void SortDoubleDimension<T>(T[,] array, bool bySecond = false)
{
    int length = array.GetLength(0);
    T[] dim1 = new T[length];
    T[] dim2 = new T[length];
    for (int i = 0; i < length; i++)
    {
        dim1[i] = array[i, 0];
        dim2[i] = array[i, 1];
    }
    if (bySecond) Array.Sort(dim2, dim1);
    else Array.Sort(dim1, dim2);
    for (int i = 0; i < length; i++)
    {
        array[i, 0] = dim1[i];
        array[i, 1] = dim2[i];
    }
}

score 0 · Answer 7 · answered Jan 15 '12 at 00:32

Why are you storing the character? You can infer it from the array index and do not need to store it! Use a one-dimensional array instead.

string encryptedText = "Test".ToUpper();
int[] frequency = new int[26];
foreach (char ch in encryptedText) {
    int charCode = ch - 'A';
    frequency[charCode]++;
}
var query = frequency
    .Select((count, index) => new { Letter = (char)(index + 'A'), Count = count })
    .Where(f => f.Count != 0)
    .OrderByDescending(f => f.Count)
    .ThenBy(f => f.Letter);
foreach (var f in query) {
    Console.WriteLine("Frequency of {0} is {1}", f.Letter, f.Count);
}

How to Sort 2D Array in C#

7 Answers7

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