Linq Distinct on specific field

Question

Given:

var s = (from p in operatorList                       
    select p.ID, p.Name,p.Phone)

How would I return the Distinct records based only on the ID?

Answer 1

If you wanted to add the ability to do this as an extension method, here's a method called DistinctBy which takes in the source and keySelector as parameters and returns the distinct item set. It does the same thing as Ahmad's second query, but looks a little prettier inline.

C#:

public static IEnumerable<TSource> DistinctBy<TSource, TKey>(
                                this IEnumerable<TSource> source, 
                                Func<TSource, TKey> keySelector)
{
    return source.GroupBy(keySelector).Select(i => i.First());
}

VB:

<Extension()>
Public Function DistinctBy(Of TSource, TKey)(
                    ByVal source As IEnumerable(Of TSource),
                    ByVal keySelector As Func(Of TSource, TKey))
                    As IEnumerable(Of TSource)

    Return source.GroupBy(keySelector).Select(Function(i) i.First())
End Function

Then call like this:

var s = (from p in operatorList.DistinctBy(x => x.ID)                       
         select p.ID, p.Name, p.Phone)