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Thread: how to join two hashsets to one hashset

  1. #1

    Thread Starter
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    how to join two hashsets to one hashset

    Hello,

    I have two hashsets of integer as below:
    Code:
    Private _ELSPropNames As New HashSet(Of Integer)
    Private _ELSPropNames1 As New HashSet(Of Integer)
    the first hashset includes 1 and 2 and the second hashset includes 1 and 3.
    I want to mix these two hashsets to one hashset but i need 1 to be included twice in my new hashset. do you know how to do it?

  2. #2
    PowerPoster techgnome's Avatar
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    Re: how to join two hashsets to one hashset

    https://learn.microsoft.com/en-us/do...h?view=net-8.0
    https://www.techiedelight.com/merge-...ets-in-csharp/

    The only problem is that you can't have the same value twice... that defeats the purpose of a hashset...the value is used to calculate the hash, which is then used as the index. So you can only have 1 in there once... because 1 will produce the same hash every time. That second link gives two examples of combining two hashsets, and that one of the values, 4, isn' duplicated despite being in both sets.


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  3. #3
    Super Moderator jmcilhinney's Avatar
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    Re: how to join two hashsets to one hashset

    Quote Originally Posted by mred View Post
    i need 1 to be included twice in my new hashset
    That's impossible. If you want duplicates then you should not be using a Hashset, at least for the combined data. You can create an array or generic List like so:
    Code:
    Dim combined = list1.Concat(list2).ToArray() 'Or .ToList()
    That will work with any two IEnumerable(Of T).

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