Can I use LINQ to check if objects in a list have a unique ID?

Question

say I have a list containing objects like this one:

public class Person
{
    private string _name; 
    private string _id;
    private int _age;

    public Person 
    {
    }

    // Accessors
}

public class ManipulatePerson
{
    Person person = new Person();
    List<Person> personList = new List<Person>;

    // Assign values

    private void PopulateList();
    {
        // Loop 
        personList.Add(person);

        // Check if every Person has a unique ID
    }
}

and I wanted to check that each Person had a unique ID. I would like to return a boolean true/false depending on whether or not the IDs are unique. Is this something I can achieve with LINQ?

Answer 1

Note that you can even leverage directly an HashSet<>:

var hs = new HashSet<string>();
bool areAllPeopleUnique = personList.All(x => hs.Add(x.Id));

(and is the code that I normally use)

It has the advantage that on the best case (presence of some duplicates) it will stop before analyzing all the personList collection.

Answer 2

I would use Distinct and then check against the counts for example:

bool bAreAllPeopleUnique = (personList.Distinct(p => p.ID).Count == personList.Count);

However as @Ian commented you will need to add a property to the Person class so that you can access the Id like so:

public string ID
{
    get { return _id; }
}

A 'nicer' way to implement this would be to add a method like so:

private bool AreAllPeopleUnique(IEnumerable<Person> people)
{
    return (personList.Distinct(p => p.ID).Count == personList.Count);
}

NOTE: The method takes in an IEnumerable not a list so that any class implementing that interface can use the method.