LINQ query to get the all the datarows based on a distinct column

Question

In VB.Net I have below LINQ Query

Dim temp = (From r In datatable Select r Order By r.str Descending)

But I want it to be unique based on str column. I know how to get just the str column from the LINQ and mark it as distinct. But I want the entire row (all columns) and have the distinct based on str column

something like

 Dim temp = (From r In datatable Select r Order By r.str Descending).distinct(r.str)

If some one can give me answer in C# I will translate it in VB.Net

Sample

datatable

col1 col2 str
A    B     X
A1   B1    Y
A2   B2    X

output should be

col1 col2 str
A     B    X
A1    B1   Y

Answer 1

If you want to select only first row from rows with same str field value:

from r in datatable.AsEnumerable()
group r by r.Field<string>("str") into g
orderby g.Key descending
select g.First()

Or method syntax

datatable.AsEnumerable()
         .GroupBy(r => r.Field<string>("str"))
         .OrderByDescending(g => g.Key)
         .Select(g => g.First())