Fastest way to Remove Duplicate Value from a list by lambda

Question

what is fastest way to remove duplicate values from a list  Assume List lt long gt  longs   new List lt long gt    1  2  3  4  3  2  5    So I am interesting in use lambda to remove duplicate and returned    1  2  3  4  5   What is your suggestion

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A simple intuitive implementation  public static List lt PointF gt  RemoveDuplicates List lt PointF gt  listPoints        List lt PointF gt  result   new List lt PointF gt          for  int i   0  i  lt  listPoints Count  i                  if   result Contains listPoints i                result Add listPoints i               return result

User · Answer

List lt long gt  distinctlongs   longs Distinct   OrderBy x   gt  x  ToList

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In-place       public static void DistinctValues lt T gt  List lt T gt  list                list Sort             int src   0          int dst   0          while  src  lt  list Count                        var val   list src               list dst    val                 dst              while    src  lt  list Count  amp  amp  list src  Equals val                       if  dst  lt  list Count                        list RemoveRange dst  list Count - dst

User · Answer

If you want to stick with the original List instead of creating a new one  you can something similar to what the Distinct   extension method does internally  i e  use a HashSet to check for uniqueness   HashSet lt long gt  set   new HashSet lt long gt  longs Count   longs RemoveAll x   gt   set Add x      The List class provides this convenient RemoveAll predicate  method that drops all elements not satisfying the condition specified by the predicate  The predicate is a delegate taking a parameter of the list s element type and returning a bool value  The HashSet s Add   method returns true only if the set doesn t contain the item yet  Thus by removing any items from the list that can t be added to the set you effectively remove all duplicates

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You can use this extension method for enumerables containing more complex types   IEnumerable lt Foo gt  distinctList   sourceList DistinctBy x   gt  x FooName    public static IEnumerable lt TSource gt  DistinctBy lt TSource  TKey gt       this IEnumerable lt TSource gt  source      Func lt TSource  TKey gt  keySelector        var knownKeys   new HashSet lt TKey gt         return source Where element   gt  knownKeys Add keySelector element

User · Answer

The easiest way to get a new list would be   List lt long gt  unique   longs Distinct   ToList      Is that good enough for you  or do you need to mutate the existing list  The latter is significantly more long-winded   Note that Distinct   isn t guaranteed to preserve the original order  but in the current implementation it will - and that s the most natural implementation  See my Edulinq blog post about Distinct   for more information   If you don t need it to be a List lt long gt   you could just keep it as   IEnumerable lt long gt  unique   longs Distinct      At this point it will go through the de-duping each time you iterate over unique though  Whether that s good or not will depend on your requirements

User · Answer

There is Distinct   method  it should works   List lt long gt  longs   new List lt long gt    1  2  3  4  3  2  5    var distinctList   longs Distinct   ToList

[c#] Fastest way to Remove Duplicate Value from a list<> by lambda

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