Remove objects with a duplicate property from List

Question

I have a List of objects in C#. All of the objects contain a property ID. There are several objects that have the same ID property.

How can I trim the List (or make a

Answer 1

MoreLINQ DistinctBy() will do the job, it allows using object proeprty for the distinctness. Unfortunatly built in LINQ Distinct() not flexible enoght.

var uniqueItems = allItems.DistinctBy(i => i.Id);

DistinctBy()

Returns all distinct elements of the given source, where "distinctness" is determined via a projection and the default eqaulity comparer for the projected type.

• Download MoreLINQ
• DistinctBy() sources

PS: Credits to Jon Skeet for sharing this library with community

Answer 2

Not sure if anyone is still looking for any additional ways to do this. But I've used this code to remove duplicates from a list of User objects based on matching ID numbers.

private ArrayList RemoveSearchDuplicates(ArrayList SearchResults)
{
    ArrayList TempList = new ArrayList();

    foreach (User u1 in SearchResults)
    {
        bool duplicatefound = false;
        foreach (User u2 in TempList)
            if (u1.ID == u2.ID)
                duplicatefound = true;

        if (!duplicatefound)
            TempList.Add(u1);
    }
    return TempList;
}

Call: SearchResults = RemoveSearchDuplicates(SearchResults);

Answer 3

If you want to avoid using a third-party library, you could do something like:

var bar = fooArray.GroupBy(x => x.Id).Select(x => x.First()).ToList();

That will group the array by the Id property, then select the first entry in the grouping.

Answer 4

var list = GetListFromSomeWhere();
var list2 = GetListFromSomeWhere();
list.AddRange(list2);

....
...
var distinctedList = list.DistinctBy(x => x.ID).ToList();

More LINQ at GitHub

Or if you don't want to use external dlls for some reason, You can use this Distinct overload:

public static IEnumerable<TSource> Distinct<TSource>(
    this IEnumerable<TSource> source, IEqualityComparer<TSource> comparer)

Usage:

public class FooComparer : IEqualityComparer<Foo>
{
    // Products are equal if their names and product numbers are equal.
    public bool Equals(Foo x, Foo y)
    {

        //Check whether the compared objects reference the same data.
        if (Object.ReferenceEquals(x, y)) return true;

        //Check whether any of the compared objects is null.
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
            return false;

        return x.ID == y.ID
    }
}



list.Distinct(new FooComparer());