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
– Marc Gravell, Commented Jan 15, 2012 at 0:00
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
– Matt Cashatt, Commented Jan 15, 2012 at 0:03
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
– L1am22, Commented Jan 15, 2012 at 0:03

Marc Gravell · Accepted Answer · 2012-01-15 00:02:38Z

17

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.

answered Jan 15, 2012 at 0:02

Marc Gravell

1.1m273 gold badges2.6k silver badges3k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Dmitry Polyanitsa · Accepted Answer · 2012-01-15 00:14:23Z

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, 2012 at 0:14

Dmitry Polyanitsa

1,0939 silver badges18 bronze badges

4 Comments

Aidiakapi Over a year ago

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

Dmitry Polyanitsa Over a year ago

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

Aidiakapi Over a year ago

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 Over a year ago

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

Rezo Megrelidze · Accepted Answer · 2013-10-15 22:29:01Z

1

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++;
        }
    }
}

answered Oct 15, 2013 at 22:29

Rezo Megrelidze

3,0801 gold badge28 silver badges30 bronze badges

Comments

Marc Gravell · Accepted Answer · 2012-01-15 00:12:30Z

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, 2012 at 0:12

Marc Gravell

1.1m273 gold badges2.6k silver badges3k bronze badges

3 Comments

Aidiakapi Over a year ago

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

Marc Gravell Over a year ago

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

Aidiakapi Over a year ago

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

Aidiakapi · Accepted Answer · 2012-01-15 00:24:25Z

0

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));

edited Jan 15, 2012 at 0:24

answered Jan 15, 2012 at 0:10

Aidiakapi

6,2594 gold badges35 silver badges64 bronze badges

Comments

Aidiakapi · Accepted Answer · 2012-01-15 00:28:47Z

0

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];
    }
}

edited Jan 15, 2012 at 0:28

answered Jan 15, 2012 at 0:22

Aidiakapi

6,2594 gold badges35 silver badges64 bronze badges

Comments

Olivier Jacot-Descombes · Accepted Answer · 2012-01-15 00:32:27Z

0

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);
}

answered Jan 15, 2012 at 0:32

Olivier Jacot-Descombes

114k14 gold badges149 silver badges202 bronze badges

Collectives™ on Stack Overflow

How to Sort 2D Array in C#

7 Answers 7

Comments

4 Comments

Comments

3 Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

Comments

4 Comments

Comments

3 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related