//initialize a dictionary with keys and values.  
Dictionary<int, string> plants = new Dictionary<int, string>() {  
  {1,"Speckled Alder"},  
  {2,"Apple of Sodom"},  
  {3,"Hairy Bittercress"},  
  {4,"Pennsylvania Blackberry"},  
  {5,"Apple of Sodom"},  
  {6,"Water Birch"},  
  {7,"Meadow Cabbage"},  
  {8,"Water Birch"}  
}; 
  
Response.Write("dictionary elements........ www.jb51.net <br />");
     
//loop dictionary all elements  
foreach (KeyValuePair<int, string> pair in plants) 
{
  Response.Write(pair.Key + "....."+ pair.Value+"<br />");
} 
  
//find dictionary duplicate values. 
var duplicateValues = plants.GroupBy(x => x.Value).Where(x => x.Count() > 1);
 
Response.Write("<br />dictionary duplicate values..........<br />");
 
//loop dictionary duplicate values only      
foreach(var item in duplicateValues) 
{
  Response.Write(item.Key+"<br />");
}