Getting unique items from a list

Question

What is the fastest   most efficient way of getting all the distinct items from a list   I have a List lt string gt  that possibly has multiple repeating items in it and only want the unique values within the list

User · Answer

You can use the Distinct method to return an IEnumerable lt T gt  of distinct items   var uniqueItems   yourList Distinct      And if you need the sequence of unique items returned as a List lt T gt   you can add a call to ToList   var uniqueItemsList   yourList Distinct   ToList

User · Answer

Apart from the Distinct extension method of LINQ  you could use a HashSet lt T gt  object that you initialise with your collection  This is most likely more efficient than the LINQ way  since it uses hash codes  GetHashCode  rather than an IEqualityComparer    In fact  if it s appropiate for your situation  I would just use a HashSet for storing the items in the first place

User · Answer

In  Net 2 0 I m pretty sure about this solution   public IEnumerable lt T gt  Distinct lt T gt  IEnumerable lt T gt  source         List lt T gt  uniques   new List lt T gt          foreach  T item in source                  if   uniques Contains item   uniques Add item               return uniques

User · Answer

You can use Distinct extension method from LINQ

User · Answer

Use a HashSet lt T gt   For example   var items    A B A D A C  Split       var unique items   new HashSet lt string gt  items   foreach  string s in unique items      Console WriteLine s     prints   A B D C

[c#] Getting unique items from a list

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