Remove objects with a duplicate property from List

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 new List) where there is only one object per ID property?

[Any additional duplicates are dropped out of the List]

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.

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

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());