Question

I have two generic Lists, one called “Featured” and the other called “Filtered”.

List<Content> Featured = new List<Content>();
List<Content> Filtered = new List<Content>();

Both contain “Content” items which are simple classes like so :

public class Content
{
    public long ContentID { get; set;}
    public string Title { get; set; }
    public string Url { get; set; }
    public string Image { get; set; }
    public string Teaser { get; set; }

    public Content(long contentId, string title, string url, string image, string teaser)
    {
        ContentID = contentId;
        Title = title;
        Url = url;
        Image = image;
    }
}

Any items that appear in “Filtered” but also appear in “Featured” need to be removed from “Filtered”. Additionally, both lists will then be combined into a single generic list with the “Featured” items appearing first.

I know I could write a couple of foreach loops to do this but I can’t help feel there must be a more elegant method using LINQ.

I am using C# 4.0.

Answer 1

If you have an IEqualityComparer defined you can use the Union method:

List<Content> FeaturedAndFiltered = Featured.Union(Filtered, new MyContentComparer());

A rough implementation of MyContentComparer would be:

public class ContentEqualityComparer : IEqualityComparer<Content>
{

    public bool Equals(Content c1, Content c2)
    {
        return (c1.ContentID == c2.ContentID);
    }


    public int GetHashCode(Content c)
    {
        return c.ContentID.GetHashCode();
    }

}