Question

我在c＃中有以下 Item 对象列表：

public class Item
{
    public int Id { get; set; }
    public List<string> Orders { get; set; }
}

List<Item> item = new List<Item>() { 
               new Item() { Id = 1, Code = 23, Orders = new List<string>() { "A", "B" }},
               new Item() { Id = 2, Code = 24, Orders = new List<string>() { "C", "D" }},
               new Item() { Id = 1, Code = 23, Orders = new List<string>() { "E", "F" }},
               new Item() { Id = 3, Code = 25, Orders = new List<string>() { "G", "H" }}
              };

我想连接其Id相同的订单，因此上面列表的输出应为：

    { 
      new Item() { Id = 1, Code = 23, Orders = new List<string>() { 'A', 'B', 'E', 'F' },
      new Item() { Id = 2, Code = 24, Orders = new List<string>() { 'C', 'D' },
      new Item() { Id = 3, Code = 25, Orders = new List<string>() { 'G', 'H' }
    };

如何在c＃中有效地完成此操作（如果可能，使用linq）？

Answer 1

您希望根据其ID对项目进行分组，然后根据该组的所有Orders创建新序列。

var query = items.GroupBy(item => item.Id)
    .Select(group => new Item
    {
        Id = group.Key,
        Orders = group.SelectMany(item => item.Orders).ToList()
    });

请注意，这不是任何数据的交集。您正在获取每个组中所有数据的 union 。

Answer 2

您可以按id对项目进行分组，然后为每个id创建新项目以连接订单：

item.GroupBy(x => x.Id)
    .Select(x => new Item
                 { 
                      Id = x.Key,     
                      Orders = x.SelectMany(a => a.Orders).ToList()
                  }).ToList();

Answer 3

看起来你想要的是这样的：

var output = items.GroupBy(i => i.Id)
                  .Select(g => new Item() 
                          {
                              Id = g.Key
                              Orders = g.SelectMany(i => i.Orders)
                                        .ToList()
                          });

或者在查询语法中：

var output = 
    from i in items
    group i by i.Id into g
    select new Item() 
           {
               Id = g.Key
               Orders = g.SelectMany(i => i.Orders).ToList()
           };

如何在c＃中列出列表？

3 个答案: