Merging every two objects into single single object making group by a property C# LINQ [closed]

Question

I have a object list like below. I want to join every two rows into single row based on column B. It is sure that only two rows would be there for every single column B value.

Input

Output

However, my solution works. but I am looking for more better solution. I am not much happy with my solution.

My solution:

var groupByItems = items.GroupBy(x => x.ColumnB).Select(x => new MappingClass
    {
        ColumnA= x.FirstOrDefault().ColumnA,
        ColumnB= x.FirstOrDefault().ColumnB,
        ColumnC= x.Where(r=> !string.IsNullOrEmpty(r.ColumnC)).Select(r=>r.ColumnC).FirstOrDefault(),
        ColumnD= x.Where(r => !string.IsNullOrEmpty(r.ColumnD)).Select(r => r.ColumnD).FirstOrDefault(),
    }).ToList();

Now groupByItems object returns me two rows as expected.

Answer 1

If you want to reduce the iteration to get the value for ColumnC and ColumnD and make the code cleaner, you can try using Aggregate instead.

var output = input
             .GroupBy(d => new {d.ColumnA, d.ColumnB})
             .Select(
                 g => g.Aggregate(
                     new MappingClass {ColumnA = g.Key.ColumnA, ColumnB = g.Key.ColumnB},
                     (result, next) =>
                     {
                         result.ColumnC ??= next.ColumnC;
                         result.ColumnD ??= next.ColumnD;
                         return result;
                     }))
              .ToList();