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Simple & Advanced Pivots with C# and ASP.NET

Nitesh Maharaj

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29 Jan 2009

How to create simple and advanced pivot tables in C# and ASP.NET

Introduction

A pivot table provides a 3 dimensional view of data. Microsoft Excel has the ability to create pivot tables, however, it's not always convenient to use Excel. You may want to create a pivot report in your web application, for example. Creating even a simple pivot table can be a complex task. So it is my intention to not only provide you with an excellent tool for creating simple and advanced pivot reports, but also to remove some of the mystery that shrouds them.

Objective

We want the ability to transform 2 dimensional data in a data table into a 3 dimensional (pivot) report.

The data table

In most instances, you'll populate a data table from a database query, like this:

SELECT 
    SalesPeople.FullName AS [Sales Person] 
    , Products.FullName AS [Product] 
    , SUM(Sales.SalesAmount) AS [Sale Amount] 
    , SUM(Sales.Qty) AS [Quantity] 
FROM 
    Sales 
JOIN 
    SalesPeople WITH (NOLOCK) 
    ON SalesPeople.SalesPersonID = Sales.SalesPersonID 
JOIN 
    Products WITH (NOLOCK) 
    ON Products.ProductCode = Sales.ProductCode 
GROUP BY 
    SalesPeople.FullName 
    , Products.FullName

The query will generate a data table like this:

Sales Person	Product	Quantity	Sale Amount
John	Pens	200	350
John	Pencils	400	500
John	Notebooks	100	300
John	Rulers	50	100
John	Calculators	120	1200
John	Back Packs	75	1500
Jane	Pens	225	393.75
Jane	Pencils	335	418.75
Jane	Notebooks	200	600
Jane	Rulers	75	150
Jane	Calculators	80	800
Jane	Back Packs	97	1940
Sally	Pens	202	353.5
Sally	Pencils	303	378.75
Sally	Notebooks	198	600
Sally	Rulers	98	594
Sally	Calculators	80	800
Sally	Back Packs	101	2020
Sarah	Pens	112	196
Sarah	Pencils	245	306.25
Sarah	Notebooks	198	594
Sarah	Rulers	50	100
Sarah	Calculators	66	660
Sarah	Back Packs	50	2020

As you can see, this is a 2 dimensional table, and it’s not very useful as a report. So we’ve got to transform this data table into something more readable.

The Pivot structure

A pivot table has 3 dimensions.

The x-axis makes up the main headings at the top of the table. The y-axis makes up the left column of the table, and the z-axis makes up the values corresponding to both the x-axis and y-axis. A simple pivot will have one z-axis column for every x-axis value, while an advanced pivot will have multiple z-axis columns per x-axis value.

A very important point is that the z-axis values can only be numeric. This is because the z-axis values are totaled horizontally and vertically. Using a non-numeric field as a z-axis field will throw an exception.

So if you look at the data table above, you’ll notice that the “Sales Person” and “Product” fields can be assigned to either the x-axis or y-axis, but not the z-axis. The “Quantity” and “Sale Amount” fields can be assigned to the z-axis.

The Pivot class

The Pivot class transforms a data table into an html table, which you can then add to a web form. Well this is just one way of implementing it. If you wish, you can create a user control with the logic from this class.

#region Variables 
    private DataTable _DataTable; 
    private string _CssTopHeading; 
    private string _CssSubHeading; 
    private string _CssLeftColumn; 
    private string _CssItems; 
    private string _CssTotals; 
    private string _CssTable; 
#endregion Variables 
#region Constructors 
public Pivot(DataTable dataTable) 
{ 
    Init(); 
    _DataTable = dataTable; 
} 
#endregion Constructors

This section of the code is pretty self explanatory. You’ll construct a Pivot object by passing a data table as an argument. The Init() method simply assigns an empty string value to the CSS variable. If the CSS variable is an empty string, the styling method will use the default style. Each of the CSS variables has a corresponding property.

private string FindValue(string xAxisField, string xAxisValue, string yAxisField, string yAxisValue, string zAxisField) 
{ 
    string zAxisValue = ""; 
    try 
    { 
        foreach (DataRow row in _DataTable.Rows) 
        { 
            if (Convert.ToString(row[xAxisField]) == xAxisValue && Convert.ToString(row[yAxisField]) == yAxisValue) 
            { 
                zAxisValue = Convert.ToString(row[zAxisField]); 
                break; 
            } 
        } 
    } 
    catch 
    { 
        throw; 
    } 
    return zAxisValue; 
}

The FindValue(…) method searches the data table for a z-axis value corresponding to the x-axis and y-axis values. The xAxisField is the column name of the x-axis field (example “Product”), and the xAxisValue is a value in that column. The yAxisField is the column name of the y-axis field (example “Sales Person”), and the yAxisValue is a value in that column. The zAxisField is the name of the column in which the z-axis value that you’re looking for resides (example “Sale Amount”).

private string[] FindValues(string xAxisField, string xAxisValue, string yAxisField, string yAxisValue, string[] zAxisFields) 
{ 
    int zAxis = zAxisFields.Length; 
    if (zAxis < 1) 
        zAxis++; 
    string[] zAxisValues = new string[zAxis]; 
    //set default values 
    for (int i = 0; i <= zAxisValues.GetUpperBound(0); i++) 
    { 
        zAxisValues[i] = "0"; 
    } 
    try 
    { 
        foreach (DataRow row in _DataTable.Rows) 
        { 
            if (Convert.ToString(row[xAxisField]) == xAxisValue && Convert.ToString(row[yAxisField]) == yAxisValue) 
            { 
                for (int z = 0; z < zAxis; z++) 
                { 
                    zAxisValues[z] = Convert.ToString(row[zAxisFields[z]]); 
                } 
                break; 
            } 
        } 
    } 
    catch 
    { 
        throw; 
    } 
    return zAxisValues; 
}

The FindValues(…) method is similar to the FindValue(…) method, however it will return multiple z-axis values. This is used for the advanced pivot table where you have multiple z-axis fields corresponding to an x-axis value.

private void MainHeaderTopCellStyle(HtmlTableCell cell) 
{ 
    if (_CssTopHeading == "") 
    { 
        cell.Style.Add("font-family", "tahoma"); 
        cell.Style.Add("font-size", "10pt"); 
        cell.Style.Add("font-weight", "normal"); 
        cell.Style.Add("background-color", "black"); 
        cell.Style.Add("color", "white"); 
        cell.Style.Add("text-align", "center"); 
    } 
    else 
        cell.Attributes.Add("Class", _CssTopHeading); 
}

This is one of the CSS styling methods. This method in particular styles the x-axis (the row at the top of the table). If you don’t assign a CSS class name to the property, the method will use the default style. The CSS class will be picked up from which ever page you add the HTML table to.

/// <summary> 
/// Creates an advanced 3D Pivot table. 
/// </summary> 
/// <param name="xAxisField">The main heading at the top of the report.</param> 
/// <param name="yAxisField">The heading on the left of the report.</param> 
/// <param name="zAxisFields">The sub heading at the top of the report.</param> 
/// <returns>HtmlTable Control.</returns> 
public HtmlTable PivotTable(string xAxisField, string yAxisField, string[] zAxisFields) 
{ 
    HtmlTable table = new HtmlTable(); 
    //style table 
    TableStyle(table); 
    /* 
    * The x-axis is the main horizontal row. 
    * The z-axis is the sub horizontal row. 
    * The y-axis is the left vertical column. 
    */ 
    try 
    { 
        //get distinct xAxisFields 
        ArrayList xAxis = new ArrayList(); 
        foreach (DataRow row in _DataTable.Rows) 
        { 
            if (!xAxis.Contains(row[xAxisField])) 
                xAxis.Add(row[xAxisField]); 
        } 
        //get distinct yAxisFields 
        ArrayList yAxis = new ArrayList(); 
        foreach (DataRow row in _DataTable.Rows) 
        { 
            if (!yAxis.Contains(row[yAxisField])) 
                yAxis.Add(row[yAxisField]); 
        } 
        //create a 2D array for the y-axis/z-axis fields 
        int zAxis = zAxisFields.Length; 
        if (zAxis < 1) 
            zAxis = 1; 
        string[,] matrix = new string[(xAxis.Count * zAxis), yAxis.Count]; 
        string[] zAxisValues = new string[zAxis]; 
        for (int y = 0; y < yAxis.Count; y++) //loop thru y-axis fields 
        { 
            //rows 
            for (int x = 0; x < xAxis.Count; x++) //loop thru x-axis fields 
            { 
                //main columns 
                //get the z-axis values 
                zAxisValues = FindValues(xAxisField, Convert.ToString(xAxis[x]) 
                    , yAxisField, Convert.ToString(yAxis[y]), zAxisFields); 
                for (int z = 0; z < zAxis; z++) //loop thru z-axis fields 
                { 
                    //sub columns 
                    matrix[(((x + 1) * zAxis - zAxis) + z), y] = zAxisValues[z]; 
                } 
            } 
        } 
        //calculate totals for the y-axis 
        decimal[] yTotals = new decimal[(xAxis.Count * zAxis)]; 
        for (int col = 0; col < (xAxis.Count * zAxis); col++) 
        { 
            yTotals[col] = 0; 
            for (int row = 0; row < yAxis.Count; row++) 
            { 
                yTotals[col] += Convert.ToDecimal(matrix[col, row]); 
            } 
        } 
        //calculate totals for the x-axis 
        decimal[,] xTotals = new decimal[zAxis, (yAxis.Count + 1)]; 
        for (int y = 0; y < yAxis.Count; y++) //loop thru the y-axis 
        { 
            int zCount = 0; 
            for (int z = 0; z < (zAxis * xAxis.Count); z++) //loop thru the z-axis 
            { 
                xTotals[zCount, y] += Convert.ToDecimal(matrix[z, y]); 
                if (zCount == (zAxis - 1)) 
                    zCount = 0; 
                else 
                    zCount++; 
            } 
        } 
        for (int xx = 0; xx < zAxis; xx++) //Grand Total 
        { 
            for (int xy = 0; xy < yAxis.Count; xy++) 
            { 
                xTotals[xx, yAxis.Count] += xTotals[xx, xy]; 
            } 
        } 
        //Build HTML Table 
        //Append main row (x-axis) 
        HtmlTableRow mainRow = new HtmlTableRow(); 
        mainRow.Cells.Add(new HtmlTableCell()); 
        for (int x = 0; x <= xAxis.Count; x++) //loop thru x-axis + 1 
        { 
            HtmlTableCell cell = new HtmlTableCell(); 
            cell.ColSpan = zAxis; 
            if (x < xAxis.Count) 
                cell.InnerText = Convert.ToString(xAxis[x]); 
            else 
                cell.InnerText = "Grand Totals"; 
            //style cell 
            MainHeaderTopCellStyle(cell); 
            mainRow.Cells.Add(cell); 
        } 
        table.Rows.Add(mainRow); 
        //Append sub row (z-axis) 
        HtmlTableRow subRow = new HtmlTableRow(); 
        subRow.Cells.Add(new HtmlTableCell()); 
        subRow.Cells[0].InnerText = yAxisField; 
        //style cell 
        SubHeaderCellStyle(subRow.Cells[0]); 
        for (int x = 0; x <= xAxis.Count; x++) //loop thru x-axis + 1 
        { 
            for (int z = 0; z < zAxis; z++) 
            { 
                HtmlTableCell cell = new HtmlTableCell(); 
                cell.InnerText = zAxisFields[z]; 
                //style cell 
                SubHeaderCellStyle(cell); 
                subRow.Cells.Add(cell); 
            } 
        } 
        table.Rows.Add(subRow); 
        //Append table items from matrix 
        for (int y = 0; y < yAxis.Count; y++) //loop thru y-axis 
        { 
            HtmlTableRow itemRow = new HtmlTableRow(); 
            for (int z = 0 ; z <= (zAxis * xAxis.Count); z++) //loop thru z-axis + 1 
            { 
                HtmlTableCell cell = new HtmlTableCell(); 
                if (z == 0) 
                { 
                    cell.InnerText = Convert.ToString(yAxis[y]); 
                    //style cell 
                    MainHeaderLeftCellStyle(cell); 
                } 
                else 
                { 
                    cell.InnerText = Convert.ToString(matrix[(z-1), y]); 
                    //style cell 
                    ItemCellStyle(cell); 
                } 
                itemRow.Cells.Add(cell); 
            } 
            //append x-axis grand totals 
            for (int z = 0; z < zAxis; z++) 
            { 
                HtmlTableCell cell = new HtmlTableCell(); 
                cell.InnerText = Convert.ToString(xTotals[z, y]); 
                //style cell 
                TotalCellStyle(cell); 
                itemRow.Cells.Add(cell); 
            } 
            table.Rows.Add(itemRow); 
        } 
        //append y-axis totals 
        HtmlTableRow totalRow = new HtmlTableRow(); 
        for (int x = 0; x <= (zAxis * xAxis.Count); x++) 
        { 
            HtmlTableCell cell = new HtmlTableCell(); 
            if (x == 0) 
                cell.InnerText = "Totals"; 
            else 
                cell.InnerText = Convert.ToString(yTotals[x-1]); 
            //style cell 
            TotalCellStyle(cell); 
            totalRow.Cells.Add(cell); 
        } 
        //append x-axis/y-axis totals 
        for (int z = 0; z < zAxis; z++) 
        { 
            HtmlTableCell cell = new HtmlTableCell(); 
            cell.InnerText = Convert.ToString(xTotals[z, xTotals.GetUpperBound(1)]); 
            //style cell 
            TotalCellStyle(cell); 
            totalRow.Cells.Add(cell); 
        } 
        table.Rows.Add(totalRow); 
    } 
    catch 
    { 
        throw; 
    } 
    return table; 
}

The PivotTable(…) method is where all the magic happens. There are two overloads of this method; one creates a simple pivot, and the other (the one above) creates an advanced pivot. The only difference is that the simple pivot has one z-axis field while the advanced pivot has more than one.

Using the Pivot class

I've included two solutions in the Pivot.zip file. The Pivot solution is a class library. You can compile the solution and reference the Pivot.dll in your web application. The other solution called PivotTest is an ASP.NET application. This shows how to implement the Pivot class.

public DataTable DataTableForTesting 
{ 
    get 
    { 
        DataTable dt = new DataTable("Sales Table"); 
        dt.Columns.Add("Sales Person"); 
        dt.Columns.Add("Product"); 
        dt.Columns.Add("Quantity"); 
        dt.Columns.Add("Sale Amount"); 
        dt.Rows.Add(new object[] { "John", "Pens", 200, 350.00 }); 
        dt.Rows.Add(new object[] { "John", "Pencils", 400, 500.00 }); 
        dt.Rows.Add(new object[] { "John", "Notebooks", 100, 300.00 }); 
        dt.Rows.Add(new object[] { "John", "Rulers", 50, 100.00 }); 
        dt.Rows.Add(new object[] { "John", "Calculators", 120, 1200.00 }); 
        dt.Rows.Add(new object[] { "John", "Back Packs", 75, 1500.00 }); 
        dt.Rows.Add(new object[] { "Jane", "Pens", 225, 393.75 }); 
        dt.Rows.Add(new object[] { "Jane", "Pencils", 335, 418.75 }); 
        dt.Rows.Add(new object[] { "Jane", "Notebooks", 200, 600.00 }); 
        dt.Rows.Add(new object[] { "Jane", "Rulers", 75, 150.00 }); 
        dt.Rows.Add(new object[] { "Jane", "Calculators", 80, 800.00 }); 
        dt.Rows.Add(new object[] { "Jane", "Back Packs", 97, 1940.00 }); 
        dt.Rows.Add(new object[] { "Sally", "Pens", 202, 353.50 }); 
        dt.Rows.Add(new object[] { "Sally", "Pencils", 303, 378.75 }); 
        dt.Rows.Add(new object[] { "Sally", "Notebooks", 198, 600.00 }); 
        dt.Rows.Add(new object[] { "Sally", "Rulers", 98, 594.00 }); 
        dt.Rows.Add(new object[] { "Sally", "Calculators", 80, 800.00 }); 
        dt.Rows.Add(new object[] { "Sally", "Back Packs", 101, 2020.00 }); 
        dt.Rows.Add(new object[] { "Sarah", "Pens", 112, 196.00 }); 
        dt.Rows.Add(new object[] { "Sarah", "Pencils", 245, 306.25 }); 
        dt.Rows.Add(new object[] { "Sarah", "Notebooks", 198, 594.00 }); 
        dt.Rows.Add(new object[] { "Sarah", "Rulers", 50, 100.00 }); 
        dt.Rows.Add(new object[] { "Sarah", "Calculators", 66, 660.00 }); 
        dt.Rows.Add(new object[] { "Sarah", "Back Packs", 50, 2020.00 }); 
        return dt; 
    } 
}

I’ve created this data table property, which builds the data table in the example above. This is just for demonstration purposes.

protected void Page_Load(object sender, EventArgs e) 
{ 
    //Advanced Pivot 
    Pivot advPivot = new Pivot(DataTableForTesting); 
    HtmlTable advancedPivot = advPivot.PivotTable("Sales Person", "Product", new string[] { "Sale Amount", "Quantity" }); 
    div1.Controls.Add(advancedPivot); 
    //Simple Pivot 
    Pivot pivot = new Pivot(DataTableForTesting); 
    //override default style with css 
    pivot.CssTopHeading = "Heading"; 
    pivot.CssLeftColumn = "LeftColumn"; 
    pivot.CssItems = "Items"; 
    pivot.CssTotals = "Totals"; 
    pivot.CssTable = "Table"; 
    HtmlTable simplePivot = pivot.PivotTable("Product", "Sales Person", "Sale Amount"); 
    div2.Controls.Add(simplePivot); 
}

The code above instantiates two pivot objects. The first is for an advanced pivot and the second is for a simple pivot. As you can see I've added the HtmlTable controls to divs. I created the divs with the runat="server" attribute so that I can access it in the code. The divs simply helps with the placement of the HtmlTable.

The advanced pivot with default styling.

	John		Jane		Sally		Sarah		Grand Totals
Product	Sale Amount	Quantity	Sale Amount	Quantity	Sale Amount	Quantity	Sale Amount	Quantity	Sale Amount	Quantity
Pens	350	200	393.75	225	353.5	202	196	112	1293.25	739
Pencils	500	400	418.75	335	378.75	303	306.25	245	1603.75	1283
Notebooks	300	100	600	200	600	198	594	198	2094	696
Rulers	100	50	150	75	594	98	100	50	944	273
Calculators	1200	120	800	80	800	80	660	66	3460	346
Back Packs	1500	75	1940	97	2020	101	2020	50	7480	323
Totals	3950	945	4302.50	1012	4746.25	982	3876.25	721	16875.00	3660

The simple pivot with custom styling using css.

Sales Person	Pens	Pencils	Notebooks	Rulers	Calculators	Back Packs	Grand Totals
John	350	500	300	100	1200	1500	3950
Jane	393.75	418.75	600	150	800	1940	4302.50
Sally	353.5	378.75	600	594	800	2020	4746.25
Sarah	196	306.25	594	100	660	2020	3876.25
Totals	1293.25	1603.75	2094	944	3460	7480	16875.00

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