Get distinct values from a column of DataTable in .NET 2.0

Question

I am working on a legacy project which was developed using .NET Framework 2.0. In this project, I get distinct values from DataRowCollection by ItemNo column. I am only interested in ItemNo. The DataRow consist of ItemNo, Qty and Date.

I am thinking of iterating the DataRowCollection and adding the unique ItemNo into a list of string as below (not tested)

var items =  new List<string>();
foreach (DataRow orderItem in rows)
{
     var itemNo = orderItem["ITEMNO"].ToString().Trim();
     if(items.Find(delegate(string str) { return str == itemNo ;}) == null)
     {
            items.Add(itemNo);
     }
 }

Is there a better way of doing this without LINQ (.Net Framework 2.0 doesnt like LINQ)

Answer 1

// Given a data table:
var dt = new DataTable();
dt.Columns.Add("ITEMNO");
dt.Rows.Add("1 ");
dt.Rows.Add(" 1");
dt.Rows.Add("2");

var dict = new Dictionary<string, bool>();

foreach(DataRow dr in dt.Rows)
{
    var itemNo = dr["ITEMNO"].ToString().Trim();

    // Take advantage of O(1) lookup:
    if (!dict.ContainsKey(itemNo))
    {
        dict.Add(itemNo, true);
    }
}

// Get list from dictionary keys:
var items = new List<string>(dict.Keys);

If you can install .Net 3.5 on the server, and reference System.Core.dll in your application, you can leverage HashSets which would modify the above code to:

var hashSet = new HashSet<string>();

foreach(DataRow dr in dt.Rows)
{
    var itemNo = dr["ITEMNO"].ToString().Trim();    

    // Only unique elements are added to the hash set, 
    // no need to check for duplicates
    hashSet.Add(itemNo);    
}

var items = new List<string>(hashSet);

The benefit of using HashSet over a Dictionary is admittedly trivial, but I'd prefer it since I don't care for the arbitrary bool value in the dictionary, but you'd need to meet the .Net 3.5 and reference requisites.