Detect duplicate records, select only the first and count using LINQ / C #

Question

I am looking for a little help in developing a query using C # / LINQ to satisfy the following requirements:

I have a list of companies: -

Id Name Email Address 1 Company A [e-mail] abc 2 Company B [e-mail] abc 3 Company C [e-mail] abc 4 Company D [e-mail] abc 5 Company A [e-mail] abc 

My goal is to detect duplicate elements based on two fields, in this example “name” and “email”.

The desired output is a list of customers, shown below:

• You can duplicate shuold customers only once.
• You must specify the number of such entries.

Desired duplicate list: -

 Id Qty Name Email Address 1 2 Company A [e-mail] abc (Id/details of first) 2 1 Company B [e-mail] abc 3 1 Company C [e-mail] abc 4 1 Company D [e-mail] abc 

Answer 1

If you explicitly want to use the record with the lowest id in each set of duplicates, you can use

 var duplicates = companies .GroupBy(c => new { c.Name, c.Email }) .Select(g => new { Qty = g.Count(), First = g.OrderBy(c => c.Id).First() } ) .Select(p => new { Id = p.First.Id, Qty = p.Qty, Name = p.First.Name, Email = p.First.Email, Address = p.First.Address }); 

If you do not care what record values ​​are used, or if your source is already sorted by ID (ascending), you can refuse to call OrderBy .

Answer 2

 from c in companies group c by new { c.Name, c.Email } into g select new { Id = g.First().Id, Qty = g.Count(), Name = g.Key.Name, Email = g.Key.Email, Address = g.First().Address };