How Get All duplicate record using linq

Question

In my project I'm having a critical problem: I have a collection of all Employees in a collection. Some of the Employees have the same LName:

public class Employee
{
    public int ID { get; set; }
    public string FName { get; set; }
    public string MName { get; set; }
    public string LName { get; set; }
    public DateTime DOB { get; set; }
    public char Gender { get; set; }
}

public class MyClass
{
    public List<Employee> GetAll()
    {
        List<Employee> empList = new List<Employee>();
        empList.Add(new Employee()
        {
            ID = 1,
            FName = "John",
            MName = "",
            LName = "Shields",
            DOB = DateTime.Parse("12/11/1971"),
            Gender = 'M'
        });
        empList.Add(new Employee()
        {
            ID = 2,
            FName = "Mary",
            MName = "Matthew",
            LName = "Jacobs",
            DOB = DateTime.Parse("01/17/1961"),
            Gender = 'F'
        });
        empList.Add(new Employee()
        {
            ID = 3,
            FName = "Amber",
            MName = "Carl",
            LName = "Agar",
            DOB = DateTime.Parse("12/23/1971"),
            Gender = 'M'
        });
        empList.Add(new Employee()
        {
            ID = 4,
            FName = "Kathy",
            MName = "",
            LName = "Foxsss",
            DOB = DateTime.Parse("11/15/1976"),
            Gender = 'F'
        });
        empList.Add(new Employee()
        {
            ID = 5,
            FName = "Lena",
            MName = "Ashco",
            LName = "Bilton",
            DOB = DateTime.Parse("05/11/1978"),
            Gender = 'F'
        });
        empList.Add(new Employee()
        {
            ID = 6,
            FName = "Susanne",
            MName = "",
            LName = "Buck",
            DOB = DateTime.Parse("03/7/1965"),
            Gender = 'F'
        });
        empList.Add(new Employee()
        {
            ID = 7,
            FName = "Jim",
            MName = "",
            LName = "Hooks",
            DOB = DateTime.Parse("09/11/1972"),
            Gender = 'M'
        });
        empList.Add(new Employee()
        {
            ID = 8,
            FName = "Jane",
            MName = "G",
            LName = "Hooks",
            DOB = DateTime.Parse("12/11/1972"),
            Gender = 'F'
        });
        empList.Add(new Employee()
        {
            ID = 9,
            FName = "Robert",
            MName = "",
            LName = "Fox",
            DOB = DateTime.Parse("06/28/1964"),
            Gender = 'M'
        });
        empList.Add(new Employee()
        {
            ID = 10,
            FName = "Cindy",
            MName = "Preston",
            LName = "Fox",
            DOB = DateTime.Parse("01/11/1978"),
            Gender = 'M'
        });

        return empList;
    }
}

How can I get the duplicate records (based on LName) from my collection using LINQ?

You should read about Collection Initializers. Also, when using object initializers, the parentheses are redundant :) — khellang
– khellang, Commented Jul 31, 2013 at 13:00

MarcinJuraszek · Accepted Answer · 2013-07-31 12:52:02Z

6

It's not clear, but looks like you're looking for following:

var duplicates = GetAll().GroupBy(x => x.LName)
                         .Where(g => g.Count() > 1)
                         .SelectMany(g => g)
                         .ToList()

It groups element by LName, takes only groups that have more than 1 element and returns them as a list.

duplicates will be List<Employee>.

You can make it a bit better using ToDictionary instead of ToList:

var duplicates = GetAll().GroupBy(x => x.LName)
                         .Where(g => g.Count() > 1)
                         .ToDictionary(g = > g.Key, g.ToList());

It will be Dictionary<string, List<Employee>>, with a LName as a dictionary key, and list of items with given LName as Value.

answered Jul 31, 2013 at 12:52

MarcinJuraszek

126k15 gold badges200 silver badges267 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

p.s.w.g Over a year ago

Why not .ToLookup(g = > g.Key)? Seems a lot cleaner than .ToDictionary(g = > g.Key, g.ToList())

MarcinJuraszek Over a year ago

@p.s.w.g Yes, it could be a lookup :)

Rajpurohit Over a year ago

@p.s.w.g sorry for that but when i use .ToLookup(g = > g.Key) then it will give me distinct duplicate record but i wont all duplicate record not distinct.

jason · Accepted Answer · 2013-07-31 13:07:25Z

1

You don't need to do a full count for a given key; you can actually be a little more efficient and still clearly express what it means for there to be a duplicate. To check for duplicates, you merely need to check that after you skip the first item, see if there are any remaining:

var duplicates = GetAll().GroupBy(x => x.LName)
                         .Where(g => g.Skip(1).Any())
                         .SelectMany(g => g);

You can convert this to a list if you need with ToList. Or you can say:

var duplicates = GetAll().GroupBy(x => x.LName)
                         .Where(g => g.Skip(1).Any())
                         .ToLookup(g => g.Key);

to have them collected by Employee.LName.

edited Jul 31, 2013 at 13:07

answered Jul 31, 2013 at 13:01

jason

243k35 gold badges436 silver badges532 bronze badges

Collectives™ on Stack Overflow

How Get All duplicate record using linq

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related