Question

I have a list which contains duplicate item values (by ID), but with a different (or possibly equal) priority. Duplicate items with same or lower priority should be removed from the list.

For example:

var items = new {
   new { Id=2, Priority=3 },
   new { Id=4, Priority=4 },
   new { Id=1, Priority=4 },
   new { Id=2, Priority=5 },
   new { Id=4, Priority=4 }
};

RemoveDuplicates(items);

// items should now contain distinct values,
// with highest possible priority
var items = new {
   new { Id=1, Priority=4 }, // this one was unique
   new { Id=2, Priority=5 }, // this one was duplicate with higher priority
   new { Id=4, Priority=4 }, // this one was duplicate with same priority
};

Is it possible to do this using LINQ? I know I could sort the list by ID and then check adjacent items, but just wanted to check if this is possible.

(update: input values are not necessarily grouped by IDs)

Answer 1

        var items = new[] {
           new { Id=2, Priority=3 },
           new { Id=2, Priority=5 },
           new { Id=1, Priority=4 },
           new { Id=4, Priority=4 },
           new { Id=4, Priority=4 }
        };

        var deduped = items
            .GroupBy(item => item.Id)
            .Select(group => group.OrderByDescending(item => item.Priority).First())
            .OrderBy(item => item.Id);