Select DISTINCT on DataTable

From:http://weblogs.asp.net/eporter/default.aspx

In a project I'm doing I needed to basically do a DISTINCT on a couple fields in a DataTable that I had used earlier in code.  Did some Google searching and came up with this MS KB on the subject.  I was hoping to find it in the Framework, but hey, writing a little extra code never hurt anyway.  Looking over the code though I found that I just didn't really like it.  Biggest reason being it only took one field.  I wanted to be able to pass in n number of fields, so I rewrote it and did a little tweaking to it.  Here's what I came up with in both VB and C#

 

 

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class SelectDistinctDataTable : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //Create table
        DataTable dt = new DataTable("items");
        //add two columns to datatable
        DataColumn col;
        col = new DataColumn("id", typeof(System.Int32));
        col.AutoIncrement = true;
        dt.Columns.Add(col);
        col = new DataColumn("item", typeof(System.String));
        dt.Columns.Add(col);
        //config AcceptChange
        dt.AcceptChanges();
        //set primary key
        dt.PrimaryKey = new DataColumn[] { dt.Columns["id"] };

        DataTable DesTbl = dt.Clone();


        DataRow dr;
        for (int i = 0; i < 10; i++)
        {
            dr = dt.NewRow();
            dr[1] = "Roboth" + i;
            dt.Rows.Add(dr);
        }
        for (int i = 0; i < 10; i++)
        {
            dr = dt.NewRow();
            dr[1] = "Roboth" + i;
            dt.Rows.Add(dr);
        }
        PrintValues(dt, "before select distinct");
        DataTable distTbl = SelectDistinct(dt, new string[] {"item" });
        PrintValues(distTbl, "the result for select distinct datatable");

    }
    private static void PrintValues(DataTable table, string lbl)
    {
        // Display the values in the supplied DataTable:

        System.Web.HttpContext.Current.Response.Write(lbl + "<br />");
        foreach (DataRow row in table.Rows)
        {
            foreach (DataColumn column in table.Columns)
            {
                System.Web.HttpContext.Current.Response.Write(row[column, DataRowVersion.Current]);
            }
            System.Web.HttpContext.Current.Response.Write("<br />");
        }
    }
    private static DataTable SelectDistinct(DataTable SourceTable, params string[] FieldNames)
    {
        object[] lastValues;
        DataTable newTable;
        DataRow[] orderedRows;

        if (FieldNames == null || FieldNames.Length == 0)
            throw new ArgumentNullException("FieldNames");

        lastValues = new object[FieldNames.Length];
        newTable = new DataTable();

        foreach (string fieldName in FieldNames)
            newTable.Columns.Add(fieldName, SourceTable.Columns[fieldName].DataType);

        orderedRows = SourceTable.Select("", string.Join(", ", FieldNames));

        foreach (DataRow row in orderedRows)
        {
            if (!fieldValuesAreEqual(lastValues, row, FieldNames))
            {
                newTable.Rows.Add(createRowClone(row, newTable.NewRow(), FieldNames));

                setLastValues(lastValues, row, FieldNames);
            }
        }

        return newTable;
    }

    private static bool fieldValuesAreEqual(object[] lastValues, DataRow currentRow, string[] fieldNames)
    {
        bool areEqual = true;
        /**//*
         id username sex
         0   1        2
         */
        for (int i = 0; i < fieldNames.Length; i++)
        {
            if (lastValues[i] == null || !lastValues[i].Equals(currentRow[fieldNames[i]]))
            {
                areEqual = false;
                break;
            }
        }

        return areEqual;
    }

    private static DataRow createRowClone(DataRow sourceRow, DataRow newRow, string[] fieldNames)
    {
        //id username sex
        // 0   1       2
        foreach (string field in fieldNames)
            newRow[field] = sourceRow[field];

        return newRow;
    }

    private static void setLastValues(object[] lastValues, DataRow sourceRow, string[] fieldNames)
    {
        //id username,sex
        // 0   1        2
        for (int i = 0; i < fieldNames.Length; i++)
            lastValues[i] = sourceRow[fieldNames[i]];
    }


}