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Get a list of different values ​​in List <T> in C #

So, let's say I have something like the following:

public class Element
{
  public int ID;
  public int Type;
  public Properties prorerty;
  ...
}
and
public class Properties
{
  public int Id;
  public string Property;
  ...
}

and I have a list of them:

List Elements = new List();

What would be the cleanest way to get a list of all the different values ​​in the prorety column in the Element class? I mean, I could iterate over the list and add all the values ​​that are not duplicated to another list of strings, but this seems dirty and inefficient. I have the feeling of some kind of magical Linq construct that will do this on one line, but I couldn't think of anything.

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5 answers
 var results = Elements.Distinct();

Note: you will have to override .Equalsand.GetHashCode()

public class Element : IEqualityComparer<Element>
{
   public bool Equals(Element x, Element y)
   {
     if (x.ID == y.ID)
     {
        return true;
     }
     else
     {
        return false;
     }
   }
}

public int GetHashCode(Element obj)
{
    return obj.ID.GetHashCode();
}
+8
source 
var props = Elements.Select(x => x.Properties).Distinct();

, .Equals() .GetHashCode().
, Properties:

var props = Elements
    .Select(x => x.Properties != null ? x.Properties.Property : null)
    .Distinct();
0

Properties, , Properties prorerty null,

IEnumerable<string> uniqueStrings = Elements
  .Select(e => e.prorerty.Property).Distinct();

prorerty , .

String, , .

0

LINQPad (# Program)

void Main()
{
    var ret = new List<Element>();
    ret.Add(new Element(){ID=1});
    ret.Add(new Element(){ID=1});
    ret.Add(new Element(){ID=2});
    ret = ret.GroupBy(x=>x.ID).Select(x=>x.First()).ToList();
    Console.WriteLine(ret.Count()); // shows 2
}

public class Element
{
  public int ID;
  public int Type;
  public Properties prorerty; 
}

public class Properties
{
  public int Id;
  public string Property;

}
0

, :)? FirstOrDefault, . : -

Comparer, , Comparer / . linq, . , :)

[TestMethod]
public void CustomDistinctTest()
{
    // Generate some sample of domain objects
    var listOfDomainObjects = Enumerable
                                .Range(10, 10)
                                .SelectMany(x => 
                                    Enumerable
                                    .Range(15, 10)
                                    .Select(y => new SomeClass { SomeText = x.ToString(), SomeInt = x + y }))
                                .ToList();

    var uniqueStringsByUsingGroupBy = listOfDomainObjects
                                    .GroupBy(x => x.SomeText)
                                    .Select(x => x.FirstOrDefault())
                                    .ToList();

    var uniqueStringsByCustomExtension = listOfDomainObjects.DistinctBy(x => x.SomeText).ToList();
    var uniqueIntsByCustomExtension = listOfDomainObjects.DistinctBy(x => x.SomeInt).ToList();

    var uniqueStrings = listOfDomainObjects
                            .Distinct(new EqualityComparerAdapter<SomeClass, string>(x => x.SomeText))
                            .OrderBy(x=>x.SomeText)
                            .ToList();

    var uniqueInts = listOfDomainObjects
                            .Distinct(new EqualityComparerAdapter<SomeClass, int>(x => x.SomeInt))
                            .OrderBy(x => x.SomeInt)
                            .ToList();
}

-:

public class EqualityComparerAdapter<T, V> : EqualityComparer<T>
    where V : IEquatable<V>
{
    private Func<T, V> _valueAdapter;

    public EqualityComparerAdapter(Func<T, V> valueAdapter)
    {
        _valueAdapter = valueAdapter;
    }

    public override bool Equals(T x, T y)
    {
        return _valueAdapter(x).Equals(_valueAdapter(y));
    }

    public override int GetHashCode(T obj)
    {
        return _valueAdapter(obj).GetHashCode();
    }
}

linq ( DistinctBy):

// Embed this class in some specific custom namespace
public static class DistByExt
{
    public static IEnumerable<T> DistinctBy<T,V>(this IEnumerable<T> enumerator,Func<T,V> valueAdapter)
        where V : IEquatable<V>
    {
        return enumerator.Distinct(new EqualityComparerAdapter<T, V>(valueAdapter));
    }
}

, :

public class SomeClass
{
    public string SomeText { get; set; }
    public int SomeInt { get; set; }

}
0

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