将指定列上的两个列表连接起来

本文关键字：两个 列表 起来 连接 | 更新日期: 2023-09-27 18:00:22

我正在尝试加入ID列上的两个列表（flist和slist）。下面显示了列表定义、类定义、列表内容和所需结果。

List<first> flist= new List<first>();
List<second> slist= new List<second>();

public class first
{
   public string name { get; set; }
   public int ID{ get; set; }
   public string itemAttr { get; set; }
}
public class second
{
   public int ID{ get; set; }
   public string itemAttr{ get; set; }
}

列出内容

flist:
apples | 1
bananas| 2
trees  | 3
slist:
1      | fruit
3      | not-fruit

期望结果：

flist:
apples   |   1     | fruit
bananas  |   2     |
trees    |   3     | not-fruit

将指定列上的两个列表连接起来

List<first> flist= new List<first>();
List<second> slist= new List<second>();
var result = from f in flist
             join s in slist on f.ID equals s.ID into g
             select new {
                 f.name,
                 f.ID,
                 itemAttr = g.Any() ? g.First().itemAttr : null
             };

试试这个

foreach(var f in first)
{
    foreach(var s in second)
    {
        if(f.ID == s.ID)
        {
            f.fAttr = item.itemAtrr;
        }
    }
}

您可以使用带有Linq:的"左外部"联接

var joined = from l1 in flist
             join l2 in slist on l1.ID equals l2.ID into gj
             from l2_sub in gj.DefaultIfEmpty()
             select new { 
                 name = l1.name, 
                 ID = l1.ID, 
                 itemAttr = l2_sub == null ? String.Empty : l2_sub.itemAttr 
             };

namespace WindowsFormsApplication26
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            List<first> flist = new List<first>();
            List<second> slist = new List<second>();
            flist.Add(new first("apples", 1));
            flist.Add(new first("bananas", 2));
            flist.Add(new first("trees", 3));
            slist.Add(new second(1, "Fruit"));
            slist.Add(new second(2, ""));
            slist.Add(new second(3, "Not-Fruit"));
            var result = (from t in flist
                          join x in slist
                          on t.ID equals x.ID
                          select new
                          {
                              Name = t.name,
                              Id = t.ID,
                              attrib = x.itemAttr
                          }).ToList();
        }

        public class first
        {
            public first()
            {
            }
            public first(string n, int id)
            {
                name = n;
                ID = id;
            }
            public string name { get; set; }
            public int ID { get; set; }
        }
        public class second
        {
            public second()
            {
            }
            public second(int id, string itm)
            {
                ID = id;
                itemAttr = itm;
            }
            public int ID { get; set; }
            public string itemAttr { get; set; }
        }
    }
}

出了什么问题？创建一个新的类，第三个类带有参数：ID，name，itemAttr。用这个类创建新的列表，并将在需要的位置写入所需的数据。

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