Not getting Distinct Items when using Linq to List?

Question

Here is how I am attempting to get a distinct List of items...

    var queryResults = PatientList.Distinct();
    PatientList = queryResults.ToList<SelectListItem>();

For some reason, I am not getting a distinct list here.

Answer 1

Use

var queryResults = PatientList.GroupBy(x=>x.Id).Select(x=>x.FirstOrDefault())
    PatientList = queryResults.ToList<SelectListItem>();

You can always try

 PatientList = PatientList.GroupBy(x=>x.Id).Select(x=>x.FirstOrDefault()).ToList<SelectListItem>();

It will give you the distinct results based off whatever you group by

Check out http://blog.jordanterrell.com/post/LINQ-Distinct()-does-not-work-as-expected.aspx

Also another question for reference: Returning a Distinct IQueryable with LINQ?

Answer 2

Not sure what kind of items your PatientList contains, but I guess you have to implement IEquatable on your custom object.

This have been aswered before here: Distinct not working with LINQ to Objects

Answer 3

Your SelectListItem class needs to override Equals and GetHashCode (and optionally implement IEquatable<SelectListItem> ). Otherwise, different instances with the same values will be considered different.

Another option is to implement a IEqualityComparer<SelectListItem> and pass it as the second parameter to Distinct .