...

private void BuildButton_Click(object sender, EventArgs e)
{
    if (data.matrixMode == RadioValues.All)
    {
	CreateMatrix(string.Empty, true);
    }
    else if (data.matrixMode == RadioValues.Speaker)
    {
	if (SpeakersListBox.SelectedIndex > -1)
	{
	    CreateMatrix(SpeakersListBox.Text, true);
	}
	else
	{
	    MessageBox.Show("You must select a speaker!", "No Speaker Selected",
		MessageBoxButtons.OK, MessageBoxIcon.Error, MessageBoxDefaultButton.Button1);
	}
    }
    else // data.matrixMode == RadioValues.Unit
    {
	if (UnitsListBox.SelectedIndex > -1)
	{
	    CreateMatrix(UnitsListBox.Text, false);
	}
	else
	{
	    MessageBox.Show("You must select a unit!", "No Unit Selected",
		MessageBoxButtons.OK, MessageBoxIcon.Error, MessageBoxDefaultButton.Button1);
	}
    }
}

...

private void CreateMatrix(string speakerOrUnit, bool isSpeaker)
{
    dataGrid.Columns.Clear();
    dataGrid.Rows.Clear();

    // Create a list of units with Bye spaces to equal number of speakers
    List<string> unitsWithByes = new List<string>(data.listUnits);

    for (int i = 0; i < (data.listSpeakers.Count - data.listUnits.Count); i++)
    {
	unitsWithByes.Add("");
    }

    // Build matrix; the rows will be contain data in the following format {speaker, month1, month2, ...};
    //  the data in the month columns is the unit the speaker will be speaking at for that month
    string[][] matrix = new string[data.listSpeakers.Count][];

    for (int i = 0; i < matrix.Length; i++)
    {
	matrix[i] = new string[data.intMonths + 1];

	matrix[i][0] = data.listSpeakers[i];

	for (int j = 0; j < data.intMonths; j++)
	{
	    matrix[i][j + 1] = unitsWithByes[(j + i) % unitsWithByes.Count];
	}
    }

    // Populate matrix columns
    string titleCol = "Speaker";

    if (!isSpeaker)
    {
	titleCol = "Unit";
    }

    dataGrid.Columns.Add(titleCol, titleCol);

    for (int i = 0; i < data.intMonths; i++)
    {
	dataGrid.Columns.Add("Month" + (i + 1), "Month" + (i + 1));
    }

    // How many rows will be displayed in matrix
    int rows = data.listSpeakers.Count;

    if (!string.IsNullOrEmpty(speakerOrUnit))
    {
	rows = 1;
    }

    // Populate matrix rows
    dataGrid.Rows.Add(rows);

    int count = 0;

    for (int i = 0; i < matrix.Length; i++)
    {
	if (string.IsNullOrEmpty(speakerOrUnit) ||
	    (isSpeaker && speakerOrUnit == matrix[i][0]) || (!isSpeaker && i == 0))
	{
	    DataGridViewRow row = dataGrid.Rows[count++];
	    row.Cells[titleCol].Value = (isSpeaker) ? matrix[i][0] : speakerOrUnit;

	    for (int j = 1; j <= data.intMonths; j++)
	    {
		string value = matrix[i][j];

		if (!isSpeaker)
		{
		    // Find speaker who has this unit in the jth month
		    for (int k = 0; k < matrix.Length; k++)
		    {
			if (matrix[k][j] == speakerOrUnit)
			{
			    value = matrix[k][0];
			}
		    }
		}

		row.Cells["Month" + j].Value = value;
	    }
	}
    }
}

...