如何在LINQ（C＃）中对不同的val进行排序？

Question

I've got this LINQ to get the distinct values of a particular class member from a generic list:

var distinctDescriptions = itemsForMonthYearList.Select(x => x.ItemDescription).Distinct();

The generic list is defined this way:

List<ItemsForMonthYear> itemsForMonthYearList;

The class is:

public class ItemsForMonthYear
{
    public String ItemDescription { get; set; }
    public String monthYr { get; set; }
    public int TotalPackages { get; set; }
    public Decimal TotalPurchases { get; set; }
    public Decimal AveragePrice { get; set; }
    public Double PercentOfTotal { get; set; }
}

I thought this would work:

var distinctDescriptions = itemsForMonthYearList.Select(x => x.ItemDescription).Distinct().OrderBy(x => x.ItemDescription);

...but it doesn't even compile:

" 'string' does not contain a definition for 'ItemDescription' and no extension method 'ItemDescription' accepting a first argument of type 'string' could be found (are you missing a using directive or an assembly reference?) "

How can I sort the distinct values alphabetically?

Answer 1

The problem is you have already projected the property ItemDescription so it is IEnumerable<String> now, so you simply need to order by it's items:-

var distinctDescriptions = itemsForMonthYearList.Select(x => x.ItemDescription)
                                                .Distinct()
                                                .OrderBy(x => x);

Answer 2

You are projecting only one property of type string , so, the result is a string collection. Try this:

var distinctDescriptions = itemsForMonthYearList.Select(x => x.ItemDescription).Distinct().OrderBy(x => x);

Answer 3

As others have already mentioned, your Select projects the property into collection of strings, and strings don't have an ItemDescription property, so you can't order by that.

Instead, you can follow the advice from this answer :

Convert the Select return collection to a List, then sort that.

var distinctDescriptions = itemsForMonthYearList.Select(x => x.ItemDescription).Distinct().ToList();
distinctDescriptions.Sort();

This will return a List<string> in sorted order.