Remove duplicate items from dropdownlist in .net

Question

How can one remove duplicate items from dropdownlist in asp.net making sure that only unique values are listed in dropdownlist

Sorry if this is the duplicate question. Searched the SO but couldn't find it.

UPDATED CODE:

 private void BindDropdown(DropDownList ddlColumn)
    {
        DataTable dtBinddropDown = new DataTable();
        DataSet dsBinddrodown = new DataSet("dsSample");
        dtBinddropDown = (DataTable)Session[GlobalConstants.SESSION_MYSESSION];
        dsBinddrodown.Tables.Add(dtBinddropDown.Copy());
        System.Collections.ArrayList arItems = new System.Collections.ArrayList();

        if (ddlColumn.ID == "ddlEntryDate")
        {
            for (int i = 1; i < dsBinddrodown.Tables[0].Rows.Count; i++)
            {
                arItems.Add(dsBinddrodown.Tables[0].Rows[i]["Column 1"].ToString());
            }
            ddlColumn.DataSource = arItems;
            ddlColumn.DataBind();
        }
}

Thanks

Solution 1

if your datasource uses a generic list, you could use LINQ to clear any duplicates before you bind it to your dropdown control - im assuming your using webforms ?

        // ******
        // Remove Any Duplicate Vehicles
        // ********************
        List<Vehicle> NoDuplicatesVehicleList = ListVehicle.AllVehicles;
        NoDuplicatesVehicleList = NoDuplicatesVehicleList.GroupBy(x => x.VehicleID).Select(x => x.First()).ToList();

this is what i have used to remove duplicate vehicle objects on my site using the VehicleID, but the same would apply to your dropdown.

hope that helps

Truegilly

Solution 2

I agree w/ Pranay's answer, but in the somewhat rare case that you don't have access to the db/sproc with the query, here's a c# based approach:

    foreach (DataRow row in dt.Rows)
    {
        string itemName = Convert.ToString(row["colname"]);
        if (dt.Select(String.Format("Colname='{0}'", itemName)).Count() > 1)
            row.Delete();
    }
    dt.AcceptChanges();

Solution 3

Try DataView.ToTable Method (Boolean, String[])

DataTable newTable = oldTable.DefaultView.ToTable(true,"{your column name}");

Solution 4

Use linq. here is an example

using System.Collections;
using System.Linq;


ArrayList inputList = new ArrayList();
ArrayList outputList = new ArrayList();
inputList.Add(1);
inputList.Add(2);
inputList.Add(3);
inputList.Add(1);

inputList.ToArray().Distinct().ToList()
            .ForEach(a => outputList.Add(a));

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