如何在具有嵌入式列表的列表上使用Linq Orderby

Question

My list contains addresses and I want to order the list accordingly. The problem I have is that in the list is a list item for street lines which permits zero or more street address lines. I can easily sequence all the other elements with this command:

**C#**
Sites == Sites.OrderBy(x => x.SiteName).ThenBy(x => x.State).ThenBy(x => x.City).ThenBy(x => x.Zip).ToList

**VB.NET**
Sites = Sites.OrderBy(Function(x) x.SiteName).ThenBy(Function(x) x.State).ThenBy(Function(x) x.City).ThenBy(Function(x) x.Zip).ToList

Most addresses contain one value in the StreetLines list but not all. The compiler allows me to add another thenby argument for Streetlines but I'm not sure what it will do. Suppose that there are multiple addresses with the values shown here:

1.  Streetline.Count = 0       
2.  Streetline.Count = 2 (0) = "1234 Main St."  (1) = "6th Floor"
3.  Streetline.Count = 1 (0) = "P.O. Box 9999"
4.  Streetline.Count = 2 (0) = "1234 Main St."  (1) = "4th Floor"
5.  Streetline.Count = 1 (0) = "101 Pacific Blvd."

Will reordering occur or will I get a runtime error? What will the sequence of the addresses be assuming that all the other single value fields are identical?

Answer 1

.OrderBy() needs to generate one single rank-able value (something which is IComparable for ordering) per element.

So if your element has a list of strings (streetlines) - you need to write a function that will generate a value / ranking string per set of streetlines.

Trivial example: Sites.OrderBy(x => x.StreetLines?.FirstOrDefault()); //picking the first available streetline

The .ThenBy() is only a secondary group sort (example if two sites had the same PO Box), and works on the same basis (single rank-able value per element).

The main thing is to figure out your data and the actual ranking scheme you want to implement.