c# - 如何在linq中进行不同的分组

Question

我有一些东西在普通的 simpel 循环中工作，但我想知道如何使用 LINQ 来完成它，如果可能的话。

我什至不知道如何描述我想做的事情。但是堆栈溢出希望我用文字而不是示例来做到这一点，所以这是我在欺骗它...

类(精简)

public class Product
{

    public int ProductId { get; set; }
    public string Name { get; set; }
    public List<CategoryGroup> CategoryGroups { get; set; }
}

public class CategoryGroup
{
    public int CategoryGroupId { get; set; }
    public string Name { get; set; }
    public List<Category> Categories { get; set; }
}

public class Category
{
    public int CategoryId { get; set; }
    public string Name { get; set; }
}

我想做什么

来自

Product 1
    CategoryGroup 1
        Category 11
        Category 12
        Category 13
    CategoryGroup 2
        Category 21
        Category 22

Product 2
    Category Group 1
        Category 11
        Category 14
    Category Group 2
        Category 21
    Category Group 3
        Category 31

到

Category Group 1
    Category 11
    Category 12
    Category 13
    Category 14
Category Group 2
    Category 21
    Category 22
Category Group 3
    Category 31

工作代码

var categoryGroups = new List<CategoryGroup>();
foreach (var product in products)
{
    foreach (var categoryGroup in product.CategoryGroups)
    {
        var group = categoryGroups.SingleOrDefault(cg => cg.CategoryGroupId == categoryGroup.CategoryGroupId);
        if (group == null)
        {
            group = new CategoryGroup {
                Categories = new List<Category>(),
                CategoryGroupId = categoryGroup.CategoryGroupId,
                Name = categoryGroup.Name
            };
            categoryGroups.Add(group);
        }

        foreach (var category in categoryGroup.Categories)
        {
            if (group.Categories.Any(c => c.CategoryId == category.CategoryId))
            {
                continue;
            }
            group.Categories.Add(category);
        }
    }
}

Answer 1

你可以通过 SelectMany 做很多子选择:

var result = products
            .SelectMany(x => x.CategoryGroups)
            .GroupBy(x => x.CategoryGroupId)
            .Select(x => new CategoryGroup
                         {
                             Categories = x.SelectMany(y => y.Categories)
                                           .Distinct(y => y.CategoryId)
                                           .OrderBy(y => y.CategoryId)
                                           .ToList(),
                             CategoryGroupId = x.Key,
                             Name = x.Values.First().Name
                         })
            .OrderBy(x => x.CategoryGroupId)
            .ToList();