How do I combine two lists using LINQ?

Question

_{Friday, May 17, 2013 9:43 AM}

Hi,

I have two lists of people i.e. List<Person>.

I want to have a final list that will have each unique person from both list A and list B.

A person who is in List A may or may not be in List B and vice versa. Therefore, the final list List C should have all the unique persons from both lists.

How can I construct this LINQ statement?

P.S. To keep things simple, the Person class has three properties i.e. PersonId, FirstName and LastName

All replies (5)

_{Friday, May 17, 2013 9:58 AM ✅Answered}

You use the Union operator

List<Person> persons1 = new List<Person>() { p1, p2, p3};
List<Person> persons2 = new List<Person>() {p3, p4 };
List<Person> uniquePersons = persons1.Union(persons2).ToList();

uniquePersons will have p1, p2, p3, & p4

---

_{Friday, May 17, 2013 10:03 AM ✅Answered}

Hi,

Check this code

List<String> list1 = new List<String>() { "A", "B", "C", "D", "E" };
List<String> list2 = new List<String>() { "B", "C", "D" };
List<String> list3 = new List<String>() { "A", "B", "C" };

var commonList = list1.Union(list2).Union(list3).Distinct();

foreach (var item in commonList)
{
    Console.WriteLine(item);
}


OUTPUT:

A
B
C
D
E

Hope it helps you.

Cheers

---

_{Friday, May 17, 2013 10:10 AM}

Thank you!

---

_{Friday, May 17, 2013 10:15 AM}

You don't need to use Distinct with the Union operator. When you Union 2 lists, you are taking only the unique values from each.

---

_{Friday, May 17, 2013 10:18 AM}

Try

public class Person
{
    public int PersonId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

protected void Page_Load(object sender, EventArgs e)
{
    var listA = new List<Person>()
    {
        new Person(){PersonId = 1, FirstName = "Nasser", LastName="Malik" },
        new Person(){PersonId = 2, FirstName = "John", LastName="Cina" },
        new Person(){PersonId = 1, FirstName = "Nasser", LastName="Malik" },
        new Person(){PersonId = 3, FirstName = "Sam", LastName="Uan" }
    };

    var listB = new List<Person>()
    {
        new Person(){PersonId = 4, FirstName = "Bill", LastName="Gates" },
        new Person(){PersonId = 1, FirstName = "Nasser", LastName="Malik" },
        new Person(){PersonId = 5, FirstName = "Phill", LastName="Jacks" }
    };

    //Get unique records if ListA has duplicate records
    var listC = listA.GroupBy(i => i.PersonId).Select(g => g.First()).ToList();

    //Add ListB records to ListC
    foreach (var person in listB)
    {
        //Check if record already exists in ListC
        if (listC.Where(a => a.PersonId == person.PersonId).Count() == 0)
        {
            listC.Add(person);
        }
    }
        

    foreach(var person in listC)
    {
        Response.Write("PersonId = " + person.PersonId + " | FirstName = " + person.FirstName + " | LastName = " + person.LastName + "</br>");
    }
}

Output:

PersonId = 1 | FirstName = Nasser | LastName = Malik
PersonId = 2 | FirstName = John | LastName = Cina
PersonId = 3 | FirstName = Sam | LastName = Uan
PersonId = 4 | FirstName = Bill | LastName = Gates
PersonId = 5 | FirstName = Phill | LastName = Jacks

Regards.