How to remove duplicate data in KeyValuePair?

Question

How to remove duplicate data when calling AddTest, remove duplicates (before adding to the list) ??
Contains need to be added, but how do I do that with List ?

private static List<KeyValuePair<byte[], string>> list = new List<KeyValuePair<byte[], string>>();

public static void AddTest(byte[] myarray, string test)
{
   list.Add(new KeyValuePair<byte[], string>(myarray, test));
}

You might want to look at https://stackoverflow.com/questions/489258/linqs-distinct-on-a-particular-property — Progman, Oct 10 '21 at 18:21
Please [edit] your question to show your attempts you have tried and the problems/error messages you get from your attempts. — Progman, Oct 10 '21 at 18:36
@AndreyVasiliykov you need to explain, what is the meaning of duplicate for you in this context — Vivek Nuna, Oct 10 '21 at 18:38

Dmitry Bychenko · Accepted Answer · 2021-10-10T19:00:26.093

First of all, we should come to terms: what are duplicates of

 KeyValuePair<byte[], string>

instances. Assuming that KeyValuePair<byte[], string> instances x and y are duplicate if and only if both Keys and Values are equal, i.e.

 x.Key.SequenceEquals(y.Key) && x.Value == y.Value

we can implement a required comparer:

public sealed class MyEquComparer : IEqualityComparer<KeyValuePair<byte[], string>> {
  public bool Equals(KeyValuePair<byte[], string> x, KeyValuePair<byte[], string> y) =>
    Enumerable.SequenceEqual(x.Key, y.Key) && string.Equals(x.Value, y.Value);

  public int GetHashCode([DisallowNull] KeyValuePair<byte[], string> obj) =>
    obj.Key == null ? 0 : obj.Key.Length;
}

And then using the comparer get rid of duplicates:

private static List<KeyValuePair<byte[], string>> list =
    new List<KeyValuePair<byte[], string>>();

private static HashSet<KeyValuePair<byte[], string>> unique = new 
    HashSet<KeyValuePair<byte[], string>>(new MyEquComparer());

public static void AddTest(byte[] myarray, string test)
{
   // only if we're adding a unique item, we put it into the list 
   if (unique.Add(test))
       list.Add(new KeyValuePair<byte[], string>(myarray, test));
}

score 0 · Answer 2 · answered Oct 10 '21 at 20:31

0

Consider using Dictionary. It allows use TryAdd that dont do anything if the dictionary already contains the Key(also it doesnt throw an Exception).

Further Informations: Here

answered Oct 10 '21 at 20:31

Davi Bertolli

71
4

score 0 · Answer 3 · answered Oct 10 '21 at 22:36

Why on earth are you using a 'List<KeyValuePair<byte[], string>>' when you could just use the Dictionary<T,T> where you determine T as your types?

Part of your problem is that you are not using the appropriate types. A List does not prevent duplicates from being added. But what you could do is check that list to see if the Key Value Pair you are adding already exists. Although this whole issue can be prevented by using TryAdd method from switching out your List<T,T> for a Dictionary.

TryAdd returns true if the key/value pair was added to the dictionary successfully; otherwise, false. Microsoft says :

Unlike the Add method, this method doesn't throw an exception if the element with the given key exists in the dictionary. Unlike the Dictionary indexer, TryAdd doesn't override the element if the element with the given key exists in the dictionary. If the key already exists, TryAdd does nothing and returns false.

And that will prevent your duplicate items from being added. More info can be read more on this here in the docs : https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2?view=net-5.0

How to remove duplicate data in KeyValuePair?

3 Answers3