Linq (或C#代码)自联接表以填充空/空值

Question

让我们假设我有一个列表，其中包含缺少值的元素，但匹配id(可能缺少或不匹配id)，因此我希望将不为空或不为空的值放入单个元素中，如果有几个值不为空，则在匹配的字段名中转换为IGrouping/list，如果没有，则转换为单个空值，

这是一个例子

     public class MyClass 
        { 
            public int vali;
            public string vala;
            public string valb;
            public long? vall;
         }

      var list = new List<MyClass>()
                {
                  new MyClass(){vali= 2,vala=null,valb="how are you",vall=7},
                  new MyClass {vali=3,vala="hi",valb="how are you doing",vall=null},
                  new MyClass{vali=2,vala="hello",valb="how are you",vall=null},
                  new MyClass{vali=3,vala=null,valb=null,vall=8},
                  new MyClass(){vali= 2,vala=null,valb=null,vall=7},
                };

我想得到以下输出

 {2,"hello",string[] {"how are you","how are you" },int[] {7,7} }
 {3 , "hi" , "how are you doing" ,8 },

使用linq

    list.GroupBy(x=>x.vali).Select(x=>x.FirstOrDefault()).ToList();

返回

 {2,"how are you",null,7},
 {3, "how are you doing",null}

那么，我可以使用什么查询，或者如何实现返回列表(或者像linq那样使用IGrouping，但编写自己的算法)

谢谢

Answer 1

有些值具有数组，而另一些值只有一个值，因此不能获得混合输出。一切都是这样或那样。

在我看来，这做了你想做的事：

var result =
    list
        .GroupBy(x => x.vali)
        .Select(gxs => new 
        {
            vali = gxs.Key,
            vala = gxs.Select(gx => gx.vala).Where(x => x != null).ToList(),
            valb = gxs.Select(gx => gx.valb).Where(x => x != null).ToList(),
            vall = gxs.Select(gx => gx.vall).Where(x => x != null).ToList(),
        })
        .ToList();

我得到：

​

​

否则，要获得单个值，请尝试如下：

List<MyClass> result =
    list
        .GroupBy(x => x.vali)
        .Select(gxs => new MyClass()
        {
            vali = gxs.Key,
            vala = gxs.Select(gx => gx.vala).Aggregate((x, y) => x ?? y),
            valb = gxs.Select(gx => gx.valb).Aggregate((x, y) => x ?? y),
            vall = gxs.Select(gx => gx.vall).Aggregate((x, y) => x ?? y),
        })
        .ToList();

使用您的数据，我得到了以下结果：

​

​

Answer 2

尝试以下几个方面：

    class Program
    {

        static void Main(string[] args)
        {
            var list = new List<MyClass>()
                {
                  new MyClass(){vali= 2,vala=null,valb="how are you",vall=7},
                  new MyClass {vali=3,vala="hi",valb="how are you doing",vall=null},
                  new MyClass{vali=2,vala="hello",valb="how are you",vall=null},
                  new MyClass{vali=3,vala=null,valb=null,vall=8},
                  new MyClass(){vali= 2,vala=null,valb=null,vall=7},
                  new MyClass(){vali= 2,vala=null,valb="how are you",vall=7},
                  new MyClass {vali=3,vala="hi",valb="how are you doing",vall=null},
                  new MyClass{vali=2,vala="hello",valb="how are you",vall=null},
                  new MyClass{vali=3,vala=null,valb=null,vall=8},
                  new MyClass(){vali= 2,vala=null,valb=null,vall=7},
                };

            var results = list.GroupBy(x => x).ToList();
          
        }
    }
    public class MyClass : IEquatable<MyClass>
    {
        public int vali;
        public string vala;
        public string valb;
        public long? vall;

        public bool Equals(MyClass other)
        {
            return
                (this.vali == other.vali) &&
                (this.vala == other.vala) &&
                (this.valb == other.valb) &&
                (this.vall == other.vall);
        }
        public override bool Equals(object obj)
        {
            return Equals(obj as MyClass);
        }
        public override int GetHashCode()
        {
            return (this.vali.ToString() + "^" + this.vala + "^" + this.valb + "^" + this.vall.ToString()).GetHashCode();
        }

    }

Answer 3

我想我找到了我想要的

使用以下查询

     var 

    list2=list.ToDictionary(x=>x).GroupBy(x=>x.Key.vali).Select(x=>new  {  
                      vali =  x.First().Key.vali,
                      vala =   x.Count(v =>  v.Value.vala !=null) > 0  ?x.Where(x=>x.Value.vala!=null).Select(x=>x.Value.vala).ToList() : new List<string> { x.FirstOrDefault(x=>x.Value.vala!=null).Value.vala },
                      valb =  x.Count(v =>  v.Value.valb !=null) > 0  ?x.Where(x=>x.Value.valb!=null).Select(x=>x.Value.valb).ToList() : new List<string> { x.FirstOrDefault(x=>x.Value.valb!=null).Value.valb },
                      vall = x.Count(v =>  v.Value.vall !=null) > 0  ?x.Where(x=>x.Value.vall!=0).Select(x=>x.Value.vall).ToList() : new List<long?> { x.FirstOrDefault(x=>x.vall!=null).Value.vall },
    
                     }).ToList();