an array with char index

[chipbu]

Hi guys,

I need some help to create an array with character indexing like this:
A B C D E ....
A 0 0 0 0 0
B 0 0 0 0 0
C 0 0 0 0 0
D 0 0 0 0 0
E 0 0 0 0 0
.
.

so that I can record the occurrence of a particular pair of letters. I tried to search on msdn but found no clue yet.
my guess is that I can use an alphabet enum to assign index to each letter. But the problem is that I cant use alphabet letter as textual data (ie string, char)
Can anybody give me a hint?

[nelo]

Hi there.

You could a two dimensional array of integers. You don't have to index with a 'char'. You can map each index to a character. For example 0 -> 'A' and so on. If you want you can define an enumeration for the alphabet. There is already System.Windows.Forms.Keys enumeration but the values there map to ASCII so you couldn't use them to index into the array. Though you could always subtrat 65 from each value...

[BigEd781]

Don't use arrays, use an associative collection:

Dictionary<char,int> tally = new Dictionary<char,int>();
foreach( char c in someString.ToCharArray( ) )
{
    if( !tally.ContainsKey( c ) )
    {
        tally.Add( c, 0 );
    }

    tally[ c ]++;
}

[rliq]

Had time to experiment. Created a CharMatrix class that should do what you want:

public class CharMatrix
{
    // row, column, value
    private Dictionary<Char, Dictionary<Char, Int32>> _matrix;

    public CharMatrix()
    {
        // empty rows with no columns, results in  Get(...) returning values of zero
        _matrix = new Dictionary<Char, Dictionary<Char, Int32>>();
    }

    /// <summary>
    /// Get a value from the Matrix
    /// </summary>
    /// <param name="row">The row index</param>
    /// <param name="column">The column index</param>
    /// <returns>The value</returns>
    public Int32 Get(Char row, Char column)
    {
        Dictionary<Char, Int32> rowVector;

        // see if row is present
        if (_matrix.TryGetValue(row, out rowVector))
        {
            // return value from column if present
            Int32 matrixValue;
            if (rowVector.TryGetValue(column, out matrixValue))
                return matrixValue;
        }

        // no column and/or no row, so return 0
        return 0;
    }

    /// <summary>
    /// Set a value in the matrix
    /// </summary>
    /// </summary>
    /// <param name="row">The row index</param>
    /// <param name="column">The column index</param>
    /// <param name="value">The value</param>
    public void Set(Char row, Char column, Int32 value)
    {
        Dictionary<Char, Int32> rowVector;

        // see if row is present
        if (_matrix.TryGetValue(row, out rowVector))
        {
            // update the value if it exists else add a new value
            if (rowVector.ContainsKey(column))
                rowVector[column] = value;
            else
                rowVector.Add(column, value);
        }
        else
        {
            // row was not present so create it, with the column value
            Dictionary<Char,Int32> newRow = new Dictionary<Char,Int32>();
            newRow.Add(column, value);

            // add it to the matrix
            _matrix.Add(row, newRow);
        }
    }

    /// <summary>
    /// Increment a value in the matrix
    /// </summary>
    /// <param name="row">The row index</param>
    /// <param name="column">the column index</param>
    public void Increment(Char row, Char column)
    {
        // neatest way, not the best performance
        Set(row, column, Get(row, column) + 1);   // easy to do Add, Subtract, Multiply etc
    }
}

Tested with...

CharMatrix matrix = new CharMatrix();

Int32 w = matrix.Get('R', 'K');    // w = 0

matrix.Set('A', 'B', 10);
Int32 x = matrix.Get('A', 'B');    // x = 10

matrix.Increment('A', 'B');
Int32 y = matrix.Get('A', 'B');    // y = 11

matrix.Increment('A', 'D');
Int32 z = matrix.Get('A', 'D');    // z = 1