How to avoid duplicate value in list Using C# in unity

Question

I am newbie in unity and use C#, actually i am python developer i try to make a list which can holds only unique Values and if some duplicate value come it will not allow to enter in list

List<int> iList = new List<int>();
    iList.Add(2);
    iList.Add(3);
    iList.Add(5);
    iList.Add(7);

list =[2,3,5,7]

**in python we just do this to avoid duplicate in list **

if(iList.indexof(value)!=-1){
iList.append(value)
}

But what should we do in C# to achieve very similar results Thanks Your effort will be highly appreciated

https://stackoverflow.com/questions/1606679/remove-duplicates-in-the-list-using-linq/38434457#38434457 — Salah Akbari, Nov 06 '17 at 20:50

score 8 · Accepted Answer · edited Nov 06 '17 at 20:36

8

C# List has similar method: if (!iList.Contains(value)) iList.Add(value);

Alternatively you can use a HashSet<int>. There you don't need to add any conditions:

var hasSet = new HashSet<int>(); 
hashSet.Add(1);
hashSet.Add(1);

edited Nov 06 '17 at 20:36

starikcetin

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answered Nov 06 '17 at 20:22

Maxim Goncharuk

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Thaks Brother Highly appreciated For time and answer – Ahmad Nov 06 '17 at 20:46
Note that using a HashSet will not preserve the order of the entries – wmebane Nov 06 '17 at 21:12

Stefan · Answer 2 · 2022-09-01T12:46:39.397

6

In C# we (can) just do this to avoid duplicate in list:

if (iList.IndexOf(value) == -1 ) {
    iList.Add(value);
}

edited Sep 01 '22 at 12:46

answered Nov 06 '17 at 20:28

Stefan

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Shouldn't the condition be `iList.IndexOf(value) == -1`? – starikcetin Nov 06 '17 at 20:37
@S.TarıkÇetin: You are right, thanks; although I don't know Phyton, maybe OP made the same mistake. – Stefan Nov 06 '17 at 21:38

Dave · Answer 3 · 2018-06-06T20:03:16.767

4

A HashSet would ensure you only have one instance of any object. Or a Dictionary if you want to have a key that is different to the object itself. Again dictionaries do not allow duplicate keys.

A HashSet will not throw an exception if you try to put in a duplicate it just won't add it.

A dictionary will throw a duplicate key exception.

edited Jun 06 '18 at 20:03

answered Nov 06 '17 at 20:24

Dave

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Note that using a HashSet/Dictionary will not preserve the order of the entries – wmebane Nov 06 '17 at 21:11

score 3 · Answer 4 · answered Nov 06 '17 at 20:25

3

Consider to build your own type of List that will never add duplicates

public class NoDuplicatesList<T> : List<T>
{
      public override Add(T Item) 
      {
         if (!Contains(item))
                base.Add(item);
      } 
}

answered Nov 06 '17 at 20:25

Nick Reshetinsky

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But HashSet is not a List actually, it has no indices and it can't get an item by index – Nick Reshetinsky Nov 06 '17 at 20:42

How to avoid duplicate value in list Using C# in unity

4 Answers4