Distinct values in linq

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I try linq query

<asp:DropDownList ID="regiondrop" runat="server" AutoPostBack="True"
onselectedindexchanged="regiondrop_SelectedIndexChanged">

I try to show distinct values in drop-down on page load. I try this query to get

What I have tried:

values

T1 tea = new T1();
var list1 = tea.t1.ToList();
var list = (from ta in list1
orderby ta.Region
select new { ta.Region,ta.RegionID }).Distinct().ToList();
but this shows all same values where as i want distinct values

in my scenario data is

RID Region
1 Paris
2 Canada
3 UK
4 Paris
5 Canada
6 London
so in this Canada and Paris 2 times so i want this 1 time in drop-down

any solution?

Posted 21-Jun-16 19:23pm

super_user

Updated 21-Jun-16 21:47pm

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Comments

Karthik_Mahalingam 22-Jun-16 1:33am

It is already distinct only [Id and region combination]
which one you will ignore. [ 1 Paris , 2 Canada ] or [4 Paris , 5 Canada ]
distinct() will not work in this way.

3 solutions

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OriginalGriff · Accepted Answer · 2016-06-21T19:49:00

Solution 1

Try Grouping them:

C#

List<T1> list1 = new List<T1>();
list1.Add(new T1 { RegionID = 1, Region = "Paris" });
list1.Add(new T1 { RegionID = 2, Region = "Canada" });
list1.Add(new T1 { RegionID = 3, Region = "UK" });
list1.Add(new T1 { RegionID = 4, Region = "Paris" });
list1.Add(new T1 { RegionID = 5, Region = "Canada" });
list1.Add(new T1 { RegionID = 6, Region = "London" });
var list = from ta in list1
            group ta by ta.Region into newgroup
            orderby newgroup.Key
            select newgroup;
foreach (var t in list)
    {
    T1 t1 = t.First();
    Console.WriteLine("{0}:{1}", t1.RegionID, t1.Region);
    }

Posted 21-Jun-16 19:49pm

OriginalGriff

Comments

super_user 22-Jun-16 2:11am

when i try this .
protected void Page_Load(object sender, EventArgs e)
{

T1 tea = new T1();
var list1 = tea.table1.ToList();
var list = from ta in list1
group ta by ta.Region into newgroup
orderby newgroup.Key
select newgroup;

this shows same output like repeated values in dropdown

if(!Page.IsPostBack)
{
regiondrop.DataSource = list;
regiondrop.DataTextField = "Region";
regiondrop.DataValueField = "RID";
regiondrop.DataBind();

}

}

OriginalGriff 22-Jun-16 2:48am

Yes...that's why my code has the call to First in the foreach...
If you want to use the list directly, change the select:

select newgroup.First();

Karthik_Mahalingam · Accepted Answer · 2016-06-21T20:19:00

Solution 2

try this

C#

var list1 = tea.t1.ToList();
     Dictionary<int, string> dict = new Dictionary<int, string>();
     foreach (var item in list1.OrderBy(k=>k.Region))
     {
         if(!dict.ContainsValue(item.Region))
         dict.Add(item.RegionID, item.Region);
     }
     var output = dict.Select(k => new { RegionId = k.Key, Region = k.Value }).ToList();

     egiondrop.DataSource = output;
     regiondrop.DataTextField = "Region";
     regiondrop.DataValueField = "RegionId";
     regiondrop.DataBind();

Posted 21-Jun-16 20:19pm

Karthik_Mahalingam

Comments

super_user 22-Jun-16 2:21am

this shows same output like repeated values in dropdown

Karthik_Mahalingam 22-Jun-16 2:23am

post the code.

super_user 22-Jun-16 2:31am

protected void Page_Load(object sender, EventArgs e)
{
T1 tea = new T1();
var list1 = tea.t1.ToList();
Dictionary<int, string=""> dict = new Dictionary<int, string="">();
foreach (var item in list1.OrderBy(k => k.Region))
{
if (!dict.ContainsValue(item.Region))
dict.Add(item.RegionID, item.Region);
}
var output = dict.Select(k => new { RegionId = k.Key, Region = k.Value }).ToList();

if(!Page.IsPostBack)
{
regiondrop.DataSource = list;
regiondrop.DataTextField = "Region";
regiondrop.DataValueField = "RegionID";
regiondrop.DataBind();

}

}

Karthik_Mahalingam 22-Jun-16 2:34am

if(!Page.IsPostBack)
{
regiondrop.DataSource = output

Maciej Los 22-Jun-16 3:05am

5ed!

Karthik_Mahalingam 22-Jun-16 3:07am

Thanks Maciej Los

super_user 22-Jun-16 3:20am

ok this is done but i dont understand these lines.. Dictionary<int, string=""> dict = new Dictionary<int, string="">();
foreach (var item in list1.OrderBy(k=>k.Region))
{
if(!dict.ContainsValue(item.Region))
dict.Add(item.RegionID, item.Region);
}

super_user 22-Jun-16 3:20am

is there any other easy method ??

Karthik_Mahalingam 22-Jun-16 3:21am

yes availble
post the class code for T1

super_user 22-Jun-16 3:24am

///