LINQ中的group操作

static void Main(string[] args)
{
    var products=new[]
        {
            new{ProductName="Apple",Category="Food"},
            new{ProductName="Cat",Category="Animal"},
            new{ProductName="Dog",Category="Other"},
            new{ProductName="Pig",Category="Animal"},
        };

    var q = from p in products
            group p by p.Category into g
            orderby g.Key
            select g;

    foreach (var item in q)
    {
        Console.WriteLine(item.Key);
        foreach (var i in item)
        {
            Console.WriteLine("\t" + i.ProductName);
        }
    }

Console.Read();

}

另外一个结合join的例子

static void Main(string[] args)
{
    NorthwindDataContext db = new NorthwindDataContext();
    var products = db.Products;
    var categorys = db.Categories;

    var query = from result in
                    from p in products.AsEnumerable()
                    join c in categorys.AsEnumerable()
                    on p.CategoryID equals c.CategoryID //这里必须写equals，而不能是=
                    select new { CategoryName = c.CategoryName, Product = p }
                group result by result.CategoryName into g
                select g;

    foreach (var group in query)
    {
        Console.WriteLine(group.Key);
        foreach (var product in group)
        {
            Console.WriteLine("\t"+product.Product.ProductName);
        }
    }
    Console.Read();

}