linq query to return distinct field values from a list of objects

Question

class obj       int typeId    10 types  0-9      string uniqueString    this is unique    Assume there is list with 100 elements of obj  but only 10 unique typeIDs  Is it possible to do write a LINQ query return the 10 unique ints from the list of objs

User · Answer

I wanted to bind a particular data to dropdown and it should be distinct. I did the following:

List<ClassDetails> classDetails;
List<string> classDetailsData = classDetails.Select(dt => dt.Data).Distinct.ToList();
ddlData.DataSource = classDetailsData;
ddlData.Databind();

See if it helps

User · Answer

Sure  use Enumerable Distinct    Given a collection of obj  e g  foo   you d do something like this   var distinctTypeIDs   foo Select x   gt  x typeID  Distinct

User · Answer

If just want to user pure Linq  you can use groupby   List lt obj gt  distinct     objs GroupBy car   gt  car typeID  Select g   gt  g First    ToList      If you want a method to be used all across the app  similar to what MoreLinq does   public static IEnumerable lt TSource gt  DistinctBy lt TSource  TKey gt       this IEnumerable lt TSource gt  source  Func lt TSource  TKey gt  keySelector        HashSet lt TKey gt  seenKeys   new HashSet lt TKey gt         foreach  TSource element in source                if   seenKeys Contains keySelector element                          seenKeys Add keySelector element                yield return element                      Using this method to find the distinct values using just the Id property  you could use   var query   objs DistinctBy p   gt  p TypeId     you can use multiple properties   var query   objs DistinctBy p   gt  new   p TypeId  p Name

User · Answer

objList Select o  gt o typeId  Distinct

User · Answer

If just want to use Linq  you can override Equals and GetHashCode methods   Product class   public class Product       public string ProductName   get  set        public int Id   get  set          public override bool Equals object obj                if    obj is Product                         return false                     var other    Product obj          return Id    other Id             public override int GetHashCode                 return Id GetHashCode              Main Method   static void Main string   args                 var products   new List lt Product gt                        new Product  ProductName  Product 1  Id   1               new Product  ProductName  Product 2  Id   2               new Product  ProductName  Product 4  Id   5               new Product  ProductName  Product 3  Id   3               new Product  ProductName  Product 4  Id   4               new Product  ProductName  Product 6  Id   4               new Product  ProductName  Product 6  Id   4                       var itemsDistinctByProductName   products Distinct   ToList             foreach  var product in itemsDistinctByProductName                        Console WriteLine   Product Id    product Id  ProductName    product ProductName                         Console ReadKey

User · Answer

I think this is what your looking for       var objs   from c in List Objects  orderby c TypeID  select c  GroupBy g  gt g TypeID  Select x  gt x FirstOrDefault             Similar to this Returning a Distinct IQueryable with LINQ

User · Answer

Assuming you want the full object  but only want to deal with distinctness by typeID  there s nothing built into LINQ to make this easy   If you just want the typeID values  it s easy - project to that with Select and then use the normal Distinct call    In MoreLINQ we have the DistinctBy operator which you could use   var distinct   list DistinctBy x   gt  x typeID     This only works for LINQ to Objects though   You can use a grouping or a lookup  it s just somewhat annoying and inefficient   var distinct   list GroupBy x   gt  x typeID   key  group    gt  group First

[c#] linq query to return distinct field values from a list of objects

Examples related to c#

Examples related to linq