C#

private void Filter_combo_SelectedIndexChanged(object sender, EventArgs e)
       {
           /* Populate the tree based on whatever the user selects to filter by
            * for example if they click on keywords then only show the keywords
            */

           string filter = Filter_combo.Text;





           using (var db = new mombooksDataContext(Properties.Settings.Default.BooksConnectionString2))
           {

               TreeNodeCollection[] nodes = new TreeNodeCollection[treeView1.Nodes.Count];
               treeView1.Nodes.CopyTo(nodes, 0);
               treeView1.Nodes.Clear();//get rid of this BEFORE we're done.
               treeView1.Nodes.AddRange(NodeBuilder.BuildNodes(treeView1.Nodes, db.Authors, db.Books, filter));

           }
       }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using momdb;

namespace Utilties
{
    public sealed class NodeBuilder
    {
        // public static void BuildNodes(TreeNodeCollection nodes,IEnumerable<Author>authors, IEnumerable<Book> books, string filter)
         public static TreeNode[] BuildNodes(TreeNodeCollection nodes,IEnumerable<Author>authors,IEnumerable<Book>books,string filter)
       {
            TreeNode node = new TreeNode();
           
            if (filter == "Keywords")
              {
                  node = nodes.Add("Keywords");
                
                  books.ToList().ForEach(m =>
                    {
                        node.Nodes.Add(m.Keywords);
                        node.Tag = filter;
                        
                        
                    });
               
            }
            if (filter == "Title")
            {
                node = nodes.Add("Title");
                books.ToList().ForEach(m =>
                    {
                        node.Nodes.Add(m.Title);
                        node.Tag = filter;
                    });
            }
           if (filter =="Author")
           {
               node = nodes.Add("Authors");
               authors = authors.ToList().Distinct();
               authors.ToList().ForEach(m =>
                {
                 node.Nodes.Add(string.Format("{0},{1}",m.AuthorFirst,m.AuthorLast));

                    //node.Nodes.Add("testing");
                    
                    node.Tag=filter;
                
                 }); 
           }
           TreeNode[] holder = new TreeNode[node.Nodes.Count];
           for (int i = 0; i < node.Nodes.Count; i++)
           {

               holder[i] = node.Nodes[i];
           }

           return holder;
        }
      
    }
}

var needed = from sRec in lstScienceStudents
       from mRec in lstMathsStudents
       where sRec.Student_Id.Equals(mRec.Student_Id)
       select new{
           Field1here = YouKnowWhat;
           Field2here = YouKnowWhat;
       }

for(rCount...){
  for(cCount...){
       str.Add(range.Cells[rCount, cCount].Value2.ToString());
  }
}

private void importDataFromExcelToolStripMenuItem_Click(object sender, EventArgs e)
 {
     /*****************************************************************************
      * allows to read file from excel
      * reference: http://csharp.net-informations.com/excel/csharp-read-excel.htm
      * ******************************************************************************/
     OpenExcelFile.Title = "SELECT EXCEL FILE TO IMPORT FROM ";
     OpenExcelFile.Filter = "XLS FILES|*.XLS";
     OpenExcelFile.InitialDirectory = @"c:\";
     string filepath = null;
     if (OpenExcelFile.ShowDialog() == DialogResult.OK)
     {
         filepath = OpenExcelFile.FileName;
     }


     Excel.Application xlApp;
     Excel.Workbook xlWorkBook;
     Excel.Worksheet xlWorkSheet;
     Excel.Range range;

     xlApp = new Excel.ApplicationClass();
     xlWorkBook = xlApp.Workbooks.Open(filepath, 0, true, 5, "", "", true,
                                        Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "\t",
                                        false, false, 0, true, 1, 0);
     xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);


     List<string> strList= new List<string>();
     string str;
     int rCount = 0;//row counter
     int cCount = 0;//column counter

     range = xlWorkSheet.UsedRange;

     for (rCount = 1; rCount <= range.Rows.Count; rCount++)
     {
         for (cCount = 1; cCount <= range.Columns.Count; cCount++)
         {
             str = (string)(range.Cells[rCount, cCount] as Excel.Range).Value2;
             strList.Add(str);

         }
     }

     xlWorkBook.Close(true, null, null);
     xlApp.Quit();

     releaseObject(xlWorkSheet);
     releaseObject(xlWorkBook);
     releaseObject(xlApp);

 }

 private void releaseObject(object obj)
 {
     try
     {
         System.Runtime.InteropServices.Marshal.ReleaseComObject(obj);
         obj = null;
     }
     catch (Exception ex)
     {
         obj = null;
         MessageBox.Show("Unable to release the Object " + ex.ToString());
     }
     finally
     {
         GC.Collect();
     }
 }

public class Something{
     public string Name{get;set;}
     public string Surname{get;set;}
     .
     .
     .
}

for(RCount...{
    curr = new Something();
    for(cCount...){
        if(c==1){
             curr.Name = (string)(range.Cells[rCount, cCount] as Excel.Range).Value2;
        }
        if(c==2){
        ...
        }
        .
        .
    }
    //now(outside the column for) add it to the list of something
    lst.Add(curr);
}

//the actual connection
                string connString = "Provider=Microsoft.Jet.OLEDB.4.0;" +
                    "Data Source=" + yourFileNameHere+ ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=2\";";
                OleDbConnection con = null;
                lst = new List<Something>();
                Something curr = new Something();

                con = new OleDbConnection(connString);
                OleDbCommand cmd = new OleDbCommand();
                cmd.Connection = con;
                cmd.CommandText = "SELECT Name,SurName,etc.. " +
                    "FROM [Sheet1$]";

                OleDbDataReader dr = null;
                try
                {
                    con.Open();
                    dr = cmd.ExecuteReader();

                    while (dr.Read())
                    {
                        curr = new Something();
                        curr.Name = dr.IsDBNull(0) ? "Empty" : dr.GetString(0);
                        curr.SurName = dr.IsDBNull(1) ? "Empty" : dr.GetString(1);
                        .
                        .
                        if (curr.IsOK())//this is really usefull
                        {
                           lst.Add(curr); 
                        }
                    }                    
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                    //posible log and stuff
                }
                finally
                {                    
                    if (con.State != ConnectionState.Closed)
                    {
                        con.Close();
                    }
                    con.Dispose();
                    con = null;
                }

var needed = from rec in lst
     where rec.Name=="YourName"
     select whateverYouNeed;