Distinct items in List using LINQ

Question

I have following class:

public class CustomerDTO
    {
            public string CardNumber { get; set; }
            public string CustomerNumber { get; set; }        
            public DateTime FetchedDate { get; private set; } = DateTime.Now;
    }

This class gets added to a List as so

    var duplicateCustomers = new List<CustomerDTO>
                {
                    new CustomerDTO { CardNumber = "123456", CustomerNumber = "1234" },
                    new CustomerDTO { CardNumber = "123456", CustomerNumber = "1234" },
                    new CustomerDTO { CardNumber = "654321", CustomerNumber = "4321" },
                    new CustomerDTO { CardNumber = "654321", CustomerNumber = "4321" }
                };

What i want to achieve is have this list filtered to distinct items so just have 2 of the four items & ensuring the FetchedDate field of the duplicate entries is the MAX one.

So all 4 items in above list would appear like following:

123456, 1234, 2018-03-16 20:17:001
123456, 1234, 2018-03-16 20:17:002
654321, 4321, 2018-03-16 20:17:003
654321, 4321, 2018-03-16 20:17:004

Then when this list is filtered (using an extension method perhaps) it would appear as so:

123456, 1234, 2018-03-16 20:17:002
654321, 4321, 2018-03-16 20:17:004

Could someone show me how to achieve this?

Possible duplicate of [LINQ's Distinct() on a particular property](https://stackoverflow.com/questions/489258/linqs-distinct-on-a-particular-property) — M.Hassan, Mar 16 '18 at 20:36

score 0 · Accepted Answer · answered Mar 16 '18 at 20:27

Try using GroupBy:

duplicateCustomers = duplicateCustomers.GroupBy(item => new 
{
    CardNumber = item.CardNumber,
    CustomerNumber = item.CustomerNumber
})
.Select(item => new CustomerDTO()
{
    CardNumber = item.Key.CardNumber,
    CustomerNumber = item.Key.CustomerNumber,
    FetchedDate = item.Max(m => m.FetchedDate)
})

score 0 · Answer 2 · answered Mar 16 '18 at 20:29

Try this:

var results = duplicateCustomers
     .GroupBy(c => new { c.CardNumber, c.CustomerNumber })
     .Select(d => d.OrderByDescending(e => e.FetchedDate)
     .First())
     .ToList();

Basically what I am doing here is using GroupBy to select distinct items on your list based on two properties, CardNumber and CustomerNumber. Then select the first results in the item results.

score 0 · Answer 3 · answered Mar 16 '18 at 21:15

You can try below code it will work for your requirement

 static void Main(string[] args)
        {
            var duplicateCustomers = new List<CustomerDTO>
                {
                    new CustomerDTO { CardNumber = "123456", CustomerNumber = "1234" },
                    new CustomerDTO { CardNumber = "123456", CustomerNumber = "1234" },
                    new CustomerDTO { CardNumber = "654321", CustomerNumber = "4321" },
                    new CustomerDTO { CardNumber = "654321", CustomerNumber = "4321" }
                };
           // var nonduplicates= duplicateCustomers.Distinct(x => x.).ToList();//duplicateCustomers.Select(x => x.CustomerNumber).Distinct().ToList();
            List<CustomerDTO> distinctCustomers = duplicateCustomers
   .GroupBy(p => p.CardNumber)
   .Select(g => g.FirstOrDefault())
   .ToList();
            foreach (var item in distinctCustomers)
            {
                Console.WriteLine("Details  "+item.CardNumber +" "+ item.CustomerNumber + "   "+item.FetchedDate);
                //Console.WriteLine("cust Number" + item.CustomerNumber);
            }

            Console.ReadLine();
        }

Distinct items in List using LINQ

3 Answers3