how can i get distinct when I have more than 2 columns?

Question

In my entity I have 4 columns A,B,C,D if i want all the columns with distinct D on it how can I do it with Linq? For example:

Col A =1  Col B=2  Col C=3  Col D=4
Col A =1  Col B=2  Col C=9  Col D=4

now when i do distinct on Col D i want to display either one of the record not both. Is there a way to do it in Linq I do not want to use looping statements to do this.

could you group the list by `D` and then do a `.First()` on it? — Gene S, Oct 30 '12 at 16:45
How do you decide which record to take? Are there any criteria or do you really just want to choose one of them at random? — goric, Oct 30 '12 at 16:50
http://stackoverflow.com/questions/1606679/remove-duplicates-in-the-list-using-linq/1606686#1606686 — Christian Hayter, Oct 30 '12 at 16:54
`data.GroupBy(x => x.D).Select(x => x.First())` as @GeneS said, — L.B, Oct 30 '12 at 17:33

score 0 · Answer 1 · answered Oct 30 '12 at 17:02

void Main()
{
    //Your provided sample data
    IEnumerable<Item> data = new Item[]
    {
        new Item{ A = 1, B = 2, C = 3, D = 4 },
        new Item{ A = 1, B = 2, C = 9, D = 4 },
    };

    //Create a custom comparer for distinct'ing
    CustomComparer comparer = new CustomComparer();

    //Use the overload for distinct
    IEnumerable<Item> distinctData = data.Distinct(comparer);

    //Now we have a distinct list according to your comparer
    foreach (var element in distinctData)
    {
        Console.WriteLine(element.C.ToString()); // => 3
    }
}

//sample class that holds your data
class Item
{
    public int A  { get; set; }
    public int B  { get; set; }
    public int C  { get; set; }
    public int D  { get; set; }
}

class CustomComparer : IEqualityComparer<Item>
{
   public bool Equals(Item x, Item y)
   {
       return x.D == y.D;
   }

   public int GetHashCode(Item obj)
   {
       return obj.D;
   }
}

Are you sure you don't want to write that simple loop :-)

how can i get distinct when I have more than 2 columns?

1 Answers1