How to Sort a List by a property in the object

Question

I have a class called Order which has properties such as OrderId, OrderDate, Quantity, and Total. I have a list of this Order class:

List<Order> objListOrder = new List<Order>();
GetOrderList(objListOrder); // fill list of orders

Now I want to sort the list based on one property of the Order object, for example I need to sort it by the order date or order id.

How can i do this in C#?

Answer 1

A Classical Object Oriented Solution

First I must genuflect to the awesomeness of LINQ.... Now that we've got that out of the way

A variation on JimmyHoffa answer. With generics the CompareTo parameter becomes type safe.

public class Order : IComparable<Order> {

    public int CompareTo( Order that ) {
        if ( that == null ) return 1;
        if ( this.OrderDate > that.OrderDate) return 1;
        if ( this.OrderDate < that.OrderDate) return -1;
        return 0;
    }
}

// in the client code
// assume myOrders is a populated List<Order>
myOrders.Sort(); 

This default sortability is re-usable of course. That is each client does not have to redundantly re-write the sorting logic. Swapping the "1" and "-1" (or the logic operators, your choice) reverses the sort order.

Answer 2

Here is a generic LINQ extension method that does not create an extra copy of the list:

public static void Sort<T,U>(this List<T> list, Func<T, U> expression)
    where U : IComparable<U>
{
    list.Sort((x, y) => expression.Invoke(x).CompareTo(expression.Invoke(y)));
}

To use it:

myList.Sort(x=> x.myProperty);

I recently built this additional one which accepts an ICompare<U>, so that you can customize the comparison. This came in handy when I needed to do a Natural string sort:

public static void Sort<T, U>(this List<T> list, Func<T, U> expression, IComparer<U> comparer)
    where U : IComparable<U>
{    
    list.Sort((x, y) => comparer.Compare(expression.Invoke(x), expression.Invoke(y)));
}

Answer 3

Using LINQ

objListOrder = GetOrderList()
                   .OrderBy(o => o.OrderDate)
                   .ToList();

objListOrder = GetOrderList()
                   .OrderBy(o => o.OrderId)
                   .ToList();

Answer 4

Make use of LiNQ OrderBy

List<Order> objListOrder=new List<Order> ();
    objListOrder=GetOrderList().OrderBy(o=>o.orderid).ToList();

Answer 5

If you need to sort the list in-place then you can use the Sort method, passing a Comparison<T> delegate:

objListOrder.Sort((x, y) => x.OrderDate.CompareTo(y.OrderDate));

If you prefer to create a new, sorted sequence rather than sort in-place then you can use LINQ's OrderBy method, as mentioned in the other answers.

Answer 6

The easiest way I can think of is to use Linq:

List<Order> SortedList = objListOrder.OrderBy(o=>o.OrderDate).ToList();