每个产品选择最后一个不可为空的项目

Question

假设我有

class Product
{
    public int Id {get; set;}
    public string Name {get; set;}
    public int Order {get; set;}
}

和我的数据有，

products[0] = new Product { Id = 1, Name = "P1", Order = 1 }; 
products[1] = new Product { Id = 1, Name = "P2", Order = 2 }; 
products[2] = new Product { Id = 1, Name = null, Order = 3 }; 
products[3] = new Product { Id = 2, Name = "P3", Order = 4 }; 
products[4] = new Product { Id = 2, Name = null, Order = 5 }; 
products[5] = new Product { Id = 2, Name = null, Order = 6 }; 

我需要的是每个Product.Id的Name的最后一个非空值(按order desc排序)。所以我的最终输出是这样的，

items[0] =  new { Id = 1, Name = "P2"}; 
items[1] =  new { Id = 2, Name = "P3"}; 

如果Id=1，我有3个名称(P1, P2, null)和非空名称(P1, P2)，但最后一个是P3。

Answer 1

这将使最后一批产品按顺序排列。

var lastOrders = products
        .Where(x => x.Name != null) // Remove inapplicable data
        .OrderBy(x => x.Order) // Order by the Order
        .GroupBy(x => x.Id) // Group the sorted Products
        .Select(x => x.Last()); // Get the last products in the groups

Answer 2

var result = products
              .GroupBy(p => p.Id)
              .Select(g => g.OrderBy(x => x.Order).Last(x => x.Name != null));

Answer 3

这将给出您想要的输出:

products.GroupBy(p => p.Id)
        .Select(g => g.OrderByDescending(gg => gg.Name)
                      .Where(gg => gg.Name != null)
                      .Select(gg => new { gg.Id, gg.Name })
                      .First());

Answer 4

这个任务可以使用下面的Linq语句来解决。

var Result = products.OrderBy().Where( null != iProduct.Name ).First();

这要求products至少包含一个Name是null的项，否则将抛出Exception。另外,

var Result = products.OrderBy().Where( null != iProduct.Name ).FirstOrDefault();

将返回null，如果products不包含此条目。

Answer 5

Try with:

var expectedProduct =products.Where(p => p.Id != null).OrderByDescending(p => p.Order).GroupBy(p => p.Id).Last()