c# LINQ - Selecting distinct sub object

Question

I have the following object structure represented by c# classes:

[
    {
        Title: "",
        Year: 1977,
        Categories: ["Action", "Adventure", "Fantasy"],
        Score: 96
    }
]

This json is serialized to an IEnumerable<TitleItem> object, where Categories is an IList<string> object.

From that collection of TitleItem objects I would like to get a new IList<string> of distinct categories. How can this be done?

Answer 1

collection.SelectMany(x=>x.Categories).District().ToList()

Answer 2

您可以使用SelectMany来“拼合”类别列表，然后使用Distinct ：

var result = titleItems.SelectMany(item => item.Categories).Distinct().ToList();

Answer 3

You can do a SelectMany and then a distinct on that IEnumerable :

IEnumerable<TitleItem> items = getItemsFromSomeWhere();
var uniqueTitles = items.SelectMany(i => i.Categories).Distinct().ToList();

Answer 4

Here is the query that will return distinct of categories

class TitleItem {
    public string Title;
    public string Year;
    public float score;
    public IList<string> Categories;
}

var titleItems = new List<TitleItem>();
var titleItem1 = new TitleItem();
titleItem1.Categories = new List<string>();
titleItem1.Categories.Add("Action");
titleItem1.Categories.Add("Adventure");
titleItem1.Categories.Add("Fantasy");
titleItem1.Categories.Add("Action");
titleItems.Add(titleItem1);

var titleItem2 = new TitleItem();
titleItem2.Categories = new List<string>();
titleItem2.Categories.Add("Action");

titleItems.SelectMany(a => a.Categories).Distinct();