CODEWITHSUNDEEP
c#listindexof
omencat
omencat

Reputation: 1165

How to use IndexOf() method of List<object>

All the examples I see of using the IndexOf() method in List<T> are of basic string types. What I want to know is how to return the index of a list type that is an object, based on one of the object variables.

List<Employee> employeeList = new List<Employee>();
employeeList.Add(new Employee("First","Last",45.00));

I want to find the index where employeeList.LastName == "Something"

Upvotes: 53

Views: 111649

Answers (6)

Soner from The Ottoman Empire
Soner from The Ottoman Empire

Reputation: 20901

The answer is for those coming here to know why IndexOf() doesn't work.

Your class must override Equals method of object possessing the following declaration.

public override bool Equals(object obj)

Upvotes: 2

PAWAN RAJ Shakya
PAWAN RAJ Shakya

Reputation: 176

I prefer like this 

    private List<Person> persons = List<Person>();

            public PersonService()
            {
                persons = new List<Person>() { 
                    new Person { Id = 1, DOB = DateTime.Today, FirstName = "Pawan", LastName = "Shakya" },
                    new Person { Id = 2, DOB = DateTime.Today, FirstName = "Bibek", LastName = "Pandey" },
                    new Person { Id = 3, DOB = DateTime.Today, FirstName = "Shrestha", LastName = "Prami" },
                    new Person { Id = 4, DOB = DateTime.Today, FirstName = "Monika", LastName = "Pandey" },
                };
            }

public PersonRepository.Interface.Person GetPerson(string lastName)
        {
            return persons[persons.FindIndex(p=>p.LastName.Equals(lastName, StringComparison.OrdinalIgnoreCase))];
        }

Upvotes: 1

Wil P
Wil P

Reputation: 3371

Sorry, one more for good measure :)

int index = employees.FindIndex(
      delegate(Employee employee)
        {
           return employee.LastName == "Something";
        });

Edit: - Full Example in .NET 2.0 Project.

class Program
{
    class Employee { public string LastName { get; set; } }
    static void Main(string[] args)
    {
        List<Employee> employeeList = new List<Employee>();
        employeeList.Add(new Employee(){LastName="Something"});
        employeeList.Add(new Employee(){LastName="Something Else"});
        int index = employeeList.FindIndex(delegate(Employee employee) 
                           { return employee.LastName.Equals("Something"); });
        Console.WriteLine("Index:{0}", index);
        Console.ReadKey();
    }
}

Upvotes: 4

Chris
Chris

Reputation: 376

public int FindIndex(Predicate<T> match);

Using lambdas:

employeeList.FindIndex(r => r.LastName.Equals("Something"));

Note: 

// Returns:
//     The zero-based index of the first occurrence of an element
//     that matches the conditions defined by match, if found; 
//     otherwise, –1.

Upvotes: 25

Sam Harwell
Sam Harwell

Reputation: 99869

int index = employeeList.FindIndex(employee => employee.LastName.Equals(somename, StringComparison.Ordinal));

Edit: Without lambdas for C# 2.0 (the original doesn't use LINQ or any .NET 3+ features, just the lambda syntax in C# 3.0):

int index = employeeList.FindIndex(
    delegate(Employee employee)
    {
        return employee.LastName.Equals(somename, StringComparison.Ordinal);
    });

Upvotes: 80

Ahmed
Ahmed

Reputation: 7238

you can do this through override Equals method

class Employee
    {
        string _name;
        string _last;
        double _val;
        public Employee(string name, string last, double  val)
        {
            _name = name;
            _last = last;
            _val = val;
        }
        public override bool Equals(object obj)
        {
            Employee e = obj as Employee;
            return e._name == _name;
        }
    }

Upvotes: 13

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