How can I sort List<T> based on properties of T?

Question

My Code looks like this :

Collection<NameValueCollection> optionInfoCollection = ....
List<NameValueCollection> optionInfoList = new List<NameValueCollection>();
optionInfoList = optionInfoCollection.ToList();

if(_isAlphabeticalSoting)
   Sort optionInfoList

I tried optionInfoList.Sort() but it is not working.

Uttasta

Answer 1

Using the sort method and lambda expressions, it is really easy.

myList.Sort((a, b) => String.Compare(a.Name, b.Name))

The above example shows how to sort by the Name property of your object type, assuming Name is of type string.

Compressed

You could just use string.Compare(a.Name, b.Name), which would be safe? – Chon

Thanks! Learn something new everyday... I'll edit the answer. – Compressed

Answer 2

If you just want Sort() to work, then you'll need to implement IComparable or IComparable<T> in the class.

If you don't mind creating a new list, you can use the OrderBy/ToList LINQ extension methods. If you want to sort the existing list with simpler syntax, you can add a few extension methods, enabling:

list.Sort(item => item.Name);

For example:

public static void Sort<TSource, TValue>(
    this List<TSource> source,
    Func<TSource, TValue> selector)
{
    var comparer = Comparer<TValue>.Default;
    source.Sort((x, y) => comparer.Compare(selector(x), selector(y)));
}
public  static void SortDescending<TSource, TValue>(
    this List<TSource> source,
    Func<TSource, TValue> selector)
{
    var comparer = Comparer<TValue>.Default;
    source.Sort((x, y) => comparer.Compare(selector(y), selector(x)));
}

Chon

Do you have an example of using these extension methods, I tried using for my question #31057758, but couldn't implement the way you have suggested – Coussoule

Answer 3

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

List<Person> people = new List<Person>();

people.Sort(
    delegate(Person x, Person y) {
        if (x == null) {
            if (y == null) { return 0; }
            return -1;
        }
        if (y == null) { return 0; }
        return x.FirstName.CompareTo(y.FirstName);
    }
);

Camarilla

Answer 4

You need to set up a comparer that tells Sort() how to arrange the items.

Check out List.Sort Method (IComparer) for an example of how to do this...

Thermolysis