如何使用LINQ Group Records和Distinct的使用

Question

given this Records

class Record
{
    DateTime Date {get; set;}
    string Article {get; set;}
    string Platform { get; set;}
    string Amount { get; set;}
}

With a sql query I get a list of Records and want to Group the Platforms by Article.

I do this query:

List<Record> recordList = FetchRecords();
var group = recordList.GroupBy(
    f => f.Article, 
    (key, g) => new 
    { 
        Article= key, 
        Platforms = g.Select(p => p.Platform).ToList() 
    });

There are around 120 different Articles and about 30 different platforms, so the expected amount of items in group is around 120 yet I am recieving thousands of items. Items in record list are a lot as its the stock of all articles in the last 30 Days so I want to get a distinct list of Articles. I just can't figure out where to do this. what am I missing?

Edit :

After further inspecting the Data at runtime I just noticed that I have it backwards. the Articles are already correctly grouped, the platforms are the ones that need to be distinct, like Astrid E was guessing in the comments

Answer 1

You can return distinct values of the Platform collection by using Enumerable.Distinct() .

The Platforms value in the result selector in your .GroupBy() operation should be computed as follows:

Platforms = g.Select(p => p.Platform).Distinct().ToList()

Answer 2

Maybe you could try something like this:

var group = recordList.GroupBy(r => r.Article)
                      .Select(a =>
                        new
                        {
                            Article = a.Key,
                            Platforms = a.GroupBy(g => g.Platform)
                        });