Distinct in Linq based on only one field of the table

Question

I am trying to use  distinct in Linq to get result based on one field of the table  so do not require a whole duplicated records from table    I know writing basic query using distinct as followed   var query    from r in table1 orderby r Text select r  distinct      but I need results where r text is not duplicated

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You can try this table1 GroupBy t   gt  t Text  Select shape   gt  shape r   Distinct

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try this code    table1 GroupBy x   gt  x Text  Select x   gt  x FirstOrDefault

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data Select x  gt x Name  Distinct   Select x   gt  new SelectListItem   Text   x

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but I need results where r text is not duplicated   Sounds as if you want this   table1 GroupBy x   gt  x Text         Where g   gt  g Count      1         Select g   gt  g First       This will select rows where the Text is unique

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There are lots of discussions around this topic   You can find one of them here    One of the most popular suggestions have been the Distinct method taking a lambda expression as a parameter as  Servy has pointed out   The chief architect of C   Anders Hejlsberg has suggested the solution here  Also explaining why the framework design team decided not to add an overload of Distinct method which takes a lambda

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Daniel Hilgarth s answer above leads to a System NotSupported exception With Entity-Framework  With Entity-Framework  it has to be   table1 GroupBy x   gt  x Text  Select x   gt  x FirstOrDefault

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From what I have found  your query is mostly correct   Just change  select r  to  select r Text  is all and that should solve the problem   This is how MSDN documented how it should work   Ex       var query    from r in table1 orderby r Text select r Text  distinct

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Try this   table1 GroupBy x   gt  x Text  Select x   gt  x FirstOrDefault       This will group the table by Text and use the first row from each groups resulting in rows where Text is distinct

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MoreLinq has a DistinctBy method that you can use   It will allow you to do   var results   table1 DistictBy row   gt  row Text     The implementation of the method  short of argument validation  is as follows   private static IEnumerable lt TSource gt  DistinctByImpl lt TSource  TKey gt  IEnumerable lt TSource gt  source      Func lt TSource  TKey gt  keySelector  IEqualityComparer lt TKey gt  comparer        HashSet lt TKey gt  knownKeys   new HashSet lt TKey gt  comparer       foreach  TSource element in source                if  knownKeys Add keySelector element                          yield return element

[c#] Distinct in Linq based on only one field of the table

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