CODEWITHSUNDEEP
c#listsearchforeach
user3213297
user3213297

Reputation: 63

How to find specific object from list in C#?

How is it possible to find a specific object from a list? Lets say i have a function that takes an object and a list that contains objects of this type and returns the number at which position the specific object is found.

The only way i could think of a solution is to run the list through with a foreach loop, but isn't there a better way?

Thanks

Upvotes: 0

Views: 1789

Answers (5)

Leonardo Festa
Leonardo Festa

Reputation: 101

You can use the IndexOf(T item) method:

myList.IndexOf(myItem);

It returns the index of the first occurrence of the item.

Upvotes: 1

Kavindu Dodanduwa
Kavindu Dodanduwa

Reputation: 13059

To see whether object is there You might just need List<T>.Contains method

It states,

Determines whether an element is in the List.

And you need to use it like List<T>.Contains(T type item) , where T is the same type of List and item you need to compare. In your case it's a the type of Object

And to return the index you can use List<T>.IndexOf Method

Searches for the specified object and returns the zero-based index of the first occurrence within the entire List.

Simple Console program 

class Program
    {
        static void Main(string[] args)
        {
            MyType a = new MyType() { id = 10 };
            MyType b = new MyType() { id = 20 };
            MyType c = new MyType() { id = 30 };

            List<MyType> testList = new List<MyType>();

            testList.Add(a);
            testList.Add(b);

            Console.WriteLine(testList.Contains(a)); // <= Will return true
            Console.WriteLine(testList.Contains(c)); // <= Will return false

            Console.WriteLine(testList.IndexOf(a)); // <= will return 0 : the index of object a

            Console.ReadKey();    
        }   
    }

    // A simple class
    class MyType
    {
        private int ID;

        public int id
        {
            get { return ID; }
            set { ID = value; }
        }
     }

Upvotes: 0

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

You can use method IndexOf or if you use a special condition then you can use method

public int FindIndex(Predicate<T> match);

where match is delegate

public delegate bool Predicate<T>(T obj);

In fact it is similar to standard C++ algorithm std::find_if

Upvotes: 0

Polynomial Proton
Polynomial Proton

Reputation: 5135

You could use linq expressions

List.where(condition)

Or 

List.Select(condition).FirstOrDefault

Based on search condition it will return the item you want.

Upvotes: 0

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726579

The only way i could think of a solution is to run the list through with a foreach loop

Generally, you need a loop (a for or foreach) to find an object in a list. You could use it directly, or through a function that iterates over list elements, but there is going to be a loop. There is no way around it: unless you know something special about the way the elements of the array are arranged, you have to look at them all.

One case of knowing something special about arrangement of elements is knowing that an array is sorted. If this is the case, and when you know the value of the attribute on which the element is sorted, you can find the element much faster by using binary search.

Upvotes: 0

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