Transfer rows to column in C#

I was having requirement to change result of SQL in such a way that rows become columns, and columns become rows.

PersonName                Year2000               Year2001               Year2002               Year2003
------------------------- ---------------------- ---------------------- -------------------    ---------------
A                         1230                   4521                   5435                   5410
B                         1330                   4231                   5435                   1200
C                         3230                   1623                   5435                   3652
D                         4230                   2321                   5435                   1859

And need output as following

SalesYear       A                      B                      C                      D
--------------- ---------------------- ---------------------- ---------------------- ----------------------
Year2000        1230                   1330                   3230                   4230
Year2001        4521                   4231                   1623                   2321
Year2001        5435                   5435                   5435                   5435
Year2001        5410                   1200                   3652                   1859

Mr Jacob wrote post on this which is uses UNPIVOT operator which is in SQL Server 2005, you can find it here.

Here is the contributed code form Abidali Suthar [one of the developer in my team], which does the same thing but in C#.

I added extension method to DataTable, by calling SwapTable method on any DataTable instance; you can get the rows in columns and columns in rows. Lets look at extension method first.

public static class DatatTableExtension
{
    /// <summary>
    /// Extension method which transform row to column and column to row
    /// </summary>
    /// <param name="dt">Object on which we have to do operation</param>
    /// <returns>Transformed DataTable object</returns>
    public static DataTable SwapTable(this DataTable dt)
    {
        if (!(dt.Columns.Count > 0 && dt.Rows.Count > 0))
            return dt;

        DataTable dtNew = new DataTable();
        dtNew.Columns.Add(dt.Columns[0].ColumnName);

        // Creating columns for new DataTable. 
        // Adding column to new data table having name as first row of old data table
        for (int i = 0; i <= dt.Rows.Count - 1; i++)
            dtNew.Columns.Add(dt.Rows[i][0].ToString());

        DataRow row;
        // Swaping the values
        for (int k = 1; k < dt.Columns.Count; k++)
        {
            row = dtNew.NewRow();
            row[0] = dt.Columns[k].ToString();
            for (int j = 1; j <= dt.Rows.Count; j++)
                row[j] = dt.Rows[j - 1][k];

            dtNew.Rows.Add(row);
        }

        return dtNew;
    }
}

As we created extension method, its now easy to call it by creating object of DataTable. Lets see with example.

protected void Page_Load(object sender, EventArgs e)
{
    using (SqlConnection con = new SqlConnection("CONNECTION_STRING"))
    {
        con.Open();
        string strSelect = "SELECT_STATEMENT";

        SqlCommand cmd = new SqlCommand(strSelect, con);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        con.Close();

        // Bind original datatable
        dgBefore.DataSource = dt;
        dgBefore.DataBind();

        // Bind swapped datatable, calling extension method on datatable5
        dgAfter.DataSource = dt.SwapTable();
        dgAfter.DataBind();
    }
}

Extension Methods in C# 3.0

Extension methods are static methods that can be invoked using instance method syntax. In effect, extension methods make it possible to extend existing types and constructed types with additional methods.
Note: Extension methods are less discoverable and more limited in functionality than instance methods. For those reasons, it is recommended that extension methods be used sparingly and only in situations where instance methods are not feasible or possible.
Extension members of other kinds, such as properties, events, and operators, are being considered but are currently not supported.
Lets see the example:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Features
{
    public static class Extensions
    {
        public static int ToInt32(this string s)
        {
            return Int32.Parse(s);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            string strTest = "1";
            Console.WriteLine(strTest.ToInt32()); //Will print 1
        }
    }
}

Now lets look close to the following statement

(this string s)

This means, method ToInt32 is applied to a variable which type is string.

So simple as that :)

Reand More on C# 3.0