Distinct in Linq based on only one field of the table

Question

I am trying to use .distinct in Linq to get result based on one field of the table (so do not require a whole duplicated records from table).

I know writing basic query using distinct as followed:

var query = (from r in table1
orderby r.Text
select r).distinct();

but I need results where r.text is not duplicated.

Answer 1

Try this:

table1.GroupBy(x => x.Text).Select(x => x.FirstOrDefault());

This will group the table by Text and use the first row from each groups resulting in rows where Text is distinct.

Answer 2

MoreLinq has a DistinctBy method that you can use:

It will allow you to do:

var results = table1.DistictBy(row => row.Text);

The implementation of the method (short of argument validation) is as follows:

private static IEnumerable<TSource> DistinctByImpl<TSource, TKey>(IEnumerable<TSource> source,
    Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
{
    HashSet<TKey> knownKeys = new HashSet<TKey>(comparer);
    foreach (TSource element in source)
    {
        if (knownKeys.Add(keySelector(element)))
        {
            yield return element;
        }
    }
}