Question

I have a object:

public class MyObject
{
int id;
string value;
}

I also have a list:

List<MyObject> list = new List<MyObject>;
for(int i=0;i;i<100000;i++)
{
list.Add(new MyObject(i, string.Format("Item {0}", i));
}

And list will be:

1, "Item 1"
2, "Item 2"
....
99999, "Item 99999"

This list is a sorted list which sorted on ID field. Note this is an example to describe a sorted list, it is not simple like the above example.

I want to find a item of ordered list based on ID field. I don’t know .NET Framework has support quickly search on a ordered list without enumerating.

I am interested in performance because of a big list. Thanks.

Best regards.

Answer 1

You can use a binary search for this.

You can use the built-in implementation, providing a custom IComparer<T> that compares on your type’s id property:

var objToFind = new MyObject { id = 42 };

int foundIndex = yourList.BinarySearch(objToFind, new MyObjectIdComparer());

// ...

public class MyObjectIdComparer : Comparer<MyObject>
{
    public override int Compare(MyObject x, MyObject y)
    {
        // argument checking etc removed for brevity

        return x.id.CompareTo(y.id);
    }
}