How do I remove duplicates from a list<listviewitem> without changing it's type?

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I have a List<listviewitem> which I will add later to my ListView with the .AddRange Method. The list contains duplicates because the entries are from different sources.

How do I remove duplicates from a List<listviewitem> without changing its type,
without changing the order of the elements,
with the usage of plain C# code (no external libraries) and without an extra coded loop for re-populating, deleting and checking?

I tried this which works for me, but the whole type is lost afterwards:

List<listviewitem> MyList = new List<listviewitem>();
//...here my List is being populated and contains duplicates... (Code not included)
List<string> tempvar = MyList.Select(x => x.Name).Distinct().ToList();

List<string> tempvar contains basically what I would need, but I need it as a List<listviewitem> not a List<string>. I am a beginner and all other stuff which I tried did not work for me like the Hashing and other sugggestions.

Later I perform the adding of the whole list to the listview as follows:
MylistView.AddRange(MyList.toArray());
After this call I would not check for duplicates anymore, the code must go before it.

What I have tried:

different suggestions for linq and distinct, nothing worked so far.

Posted 14-Mar-16 7:41am

ByeByeByeByeBye

Updated 14-Mar-16 9:08am

Sascha Lefèvre

v2

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Sergey Alexandrovich Kryukov 21-Apr-16 21:07pm

Why not preventing duplicates in first place, when you add items?
—SA

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Matt T Heffron · Answer 1 · 2016-03-14T09:08:00

My first suggestion, if possible, would be to collect the list of distinct data first and then go from there to create a ListViewItem for each.

Another way:
Try using the version of .Distinct() that takes an IEqualityComparer<TSource> parameter.
Like:

C#

class LviNameComparer : IEqualityComparer<ListViewItem>
{
  // implement Equals and GetHashCode methods of the interface
  public bool Equals(ListViewItem lvi1, ListViewItem lvi2)
  {
    return ReferenceEquals(lvi1, lvi2) ||
           (lvi1 != null &&
            lvi2 != null &&
            lvi1.Name.Equals(lvi2.Name));
  }

  public int GetHashCode(ListViewItem lvi)
  {
    return lvi == null ? 
           0 :
           (lvi.Name ?? string.Empty).GetHashCode();
  }
}

List<string> tempvar = MyList.Distinct(new LviNameComparer()).ToList();

Sascha Lefèvre · Answer 2 · 2016-03-14T07:52:00

You're basically looking for a .DistinctBy(..) method, which isn't included in standard .NET but there are implementations, one of which you can find here:
GitHub - morelinq/MoreLINQ: Extensions to LINQ to Objects[^]

..which will allow you to do this:

C#

List<listviewitem> distinctItems = MyList.DistinctBy(x => x.Name).ToList();

Edit:
If you don't want to include the whole MoreLINQ-project into your solution, use just the following code and copy it into its own C#-source-file:

C#

using System;
using System.Collections.Generic;

namespace LinqExtensions
{
    public static class LinqExtensionDistinctBy
    {
        public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        {
            HashSet<TKey> keys = new HashSet<TKey>();

            foreach (TSource item in source)
            {
                if (keys.Add(keySelector(item)))
                {
                    yield return item;
                }
            }
        }
    }
}

Add a using LinqExtensions; -directive to your files where you want to use this extension method.

How do I remove duplicates from a list<listviewitem> without changing it's type?

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