根据最高价值从列表中获取前5名

Question

I have a list which is made up of two items postcode and totalCost. I want to grab the top 5 items from this list which have the highest total cost. I have tried

var top5 = list.Take(5).OrderByDescending(a => a.TotalCost);

also

var top5 = list.OrderByDescending(a=> a.TotalCost).Take(5);

Neither of these queries produce anything in var called top5. What is wrong with this syntax please?

Answer 1

 var i = sums.OrderByDescending(x => x.TotalCost).Take(5).ToList();

    foreach (var postCodeSum in i)
    {
        Console.WriteLine(postCodeSum.TotalCost);
    }

EDIT: Didn't realise you wanted the highest values, edited the code; I've ran the code and it should work just fine.

Answer 2

LINQ can be used :

.OrderByDescending(x => x.TotalCost).Take(5).ToList();

The problem is the .ToList() you forgot.

Answer 3

The supplied query( OrderByDescending followed by Take() )should work, make sure that the property/fileds in the class are public. I'm answering based on the comment

The PostCodeSum class only contains private decimal _totalCost; private string _postCode; – Giraffe 4 m

If it is private as you mentioned you will definitely get compilation error at a.TotalCost in the query. if the properties are accessible means the following code will work:

var top5 = postCodeSumTotals.OrderByDescending(a => a.TotalCost).Take(5); 

Take a look at this Working Example

Answer 4

Resolved it by putting the result into a list instead. Not sure why the other way didn't work.

List<PostCodeSum> postCodeSumTotalsFinal = postCodeSumTotals.OrderByDescending(o => o.TotalCost).Take(5).ToList();