Question

我的列表内容如下，

List<MyData> DICT_list = new List<MyData>()
{
   new MyData{ Dictionay="Alpha", Dimension="Length", Classes=null},
   new MyData{ Dictionay="Alpha", Dimension="Length", Classes="Process"},
   new MyData{ Dictionay="Alpha", Dimension="breath", Classes="Activity"},
   new MyData{ Dictionay="Alpha", Dimension="Height", Classes="Workflow"},
   new MyData{ Dictionay="Beta", Dimension="Height", Classes=null},
   new MyData{ Dictionay="Beta", Dimension="Height", Classes="Workflow"},
   new MyData{ Dictionay="Beta", Dimension="Length", Classes="Workflow"}
};

我希望获得数据，例如如下，

 Want to get All the Classes of Dimension=length in dictionary=ALPHA only...

非常感谢任何帮助。

---------有问题的更新-------

public struct MyData
        {
            public string Dictionary { get; set; }
            public string Dimension { get; set; }
            public string Classes { get; set; }
        }

并执行如下，

var SelectedValue = DICT_list.Where(d => d.Dimension == "Length" && d.Dictionary == "Alpha").Select(d => d.Class);
                foreach (var value in SelectedValue)
                {
                    MessageBox.Show(value.ToString());
                }

我在第MessageBox.show(value.ToString);行收到跟踪错误

Object Reference not set to instance of an object

我的列表中包含了所需的元素，我已通过以下命令对其进行了测试，

string count = DICT_list.Count.ToString(); // Here count gives the value 14 which has the desired Dictionary and DImension name along with several classes which I need to fetch..

-------------------更新了问题---------

我想我知道为什么这个错误（如果我没错）是因为我的新维度的类的第一个值在List中是空的，我很抱歉错误的问题，现在通过测试了解，我可以做一些忽略空值并从列表中移动到下一步的东西。

Answer 1

首先 - 只需按Dimension 和 Dictionay过滤列表。第二 - 仅通过选择Classes从结果中投射每个项目。这会给你IEnumerable<string>：

var query = DICT_list.Where(d => d.Dimension == "Length" && d.Dictionay == "Aplha")
                     .Select(d => d.Classes);

或查询语法：

var query = from d in DICT_list
            where d.Dimension == "Length" && d.Dictionay == "Aplha"
            select d.Classes;

我建议你看看Basic LINQ Query Operations (C#)

Answer 2

@Sergey Berezovskiy给出的解决方案正常工作。这是一个证明。

class Program
{
    static void Main(string[] args)
    {

        List<MyData> DICT_list = new List<MyData>()
        {
           new MyData{ Dictionay="Aplha", Dimension="Length", Classes="Process"},
           new MyData{ Dictionay="Aplha", Dimension="breath", Classes="Activity"},
           new MyData{ Dictionay="Aplha", Dimension="Height", Classes="Workflow"},
           new MyData{ Dictionay="Beta", Dimension="Height", Classes="Workflow"},
           new MyData{ Dictionay="Beta", Dimension="Length", Classes="Workflow"}
        };

        var query = DICT_list.Where(d => d.Dimension == "Length" && d.Dictionay == "Aplha")
                 .Select(d => d.Classes);

        foreach (var VARIABLE in query)
        {
            Console.WriteLine(VARIABLE.ToString());
        }


        Console.ReadLine();
    }
}

输出：处理

后续问题的详尽答案：“我可以做一些忽略空值并从列表中移动到下一步的内容。”

此查询可能对您有所帮助：

var query = DICT_list.Where(d => d.Dimension == "Length" && d.Dictionay == 
"Aplha" && d.Classes != null).Select(d => d.Classes);

从列表中获取特定属性

2 个答案: