如何使用LINQ对字典中的键列表进行过滤

本文关键字：列表 过滤 何使用 LINQ 字典 | 更新日期: 2023-09-27 18:13:27

我将这个字典mappings声明为Dictionary<string, HashSet<string>>。
我还有这个方法对字典中的哈希集做一些事情:

public void DoStuff(string key, int iClassId){
    foreach (var classEntry in
             from c in mappings[key]
             where c.StartsWith(iClassId + "(")
             select c)
    {
        DoStuffWithEntry(classEntry);
    }
}
private void DoStuffWithEntry(string classEntry){
    // Do stuff with classEntry here
}

在一种情况下，我需要在映射字典中的许多键上这样做，我认为最好重写和过滤键列表，而不是为每个键调用DoStuff来优化执行。

目前我这样做:

DoStuff("key1", 123);
DoStuff("key2", 123);
DoStuff("key4", 123);
DoStuff("key7", 123);
DoStuff("key11", 123);

逻辑上类似于这样的东西，而不是为每个调用DoStuff (FilterOnKeys不是一个方法-只是我想要的…):

    foreach (var classEntry in
             from c in mappings.FilterOnKeys("key1", "key2", "key4", "key7", "key11")
             where c.StartsWith(iClassId + "(")
             select c)
    {
        DoStuffWithEntry(classEntry);
    }

如何使用LINQ对字典中的键列表进行过滤

听起来你想:

string[] keys = { "key1", "key2", ... }
var query = from key in keys
            from c in mappings[key]
            ...;
foreach (var entry in query)
{
    ...
}

(我个人会为查询使用单独的变量只是为了可读性-我不太热衷于foreach循环的声明位变得巨大。)

我按照您的要求使用LINQ 

var temp = eid.Select(i => 
            EmployeeList.ContainsKey(i) 
            ? EmployeeList[i]
            : null
        ).Where(i => i != null).ToList();

完整的c#源代码是

public class Person
{
    public int EmpID { get; set; }
    public string Name { get; set; }
    public string Department { get; set; }
    public string Gender { get; set; }
}
void Main()
{   
    Dictionary<int, Person> EmployeeList = new Dictionary<int, Person>();
    EmployeeList.Add(1, new Person() {EmpID = 1, Name = "Peter", Department = "Development",Gender = "Male"});
    EmployeeList.Add(2, new Person() {EmpID = 2, Name = "Emma Watson", Department = "Development",Gender = "Female"});
    EmployeeList.Add(3, new Person() {EmpID = 3, Name = "Raj", Department = "Development",Gender = "Male"});
    EmployeeList.Add(4, new Person() {EmpID = 4, Name = "Kaliya", Department = "Development",Gender = "Male"});
    EmployeeList.Add(5, new Person() {EmpID = 5, Name = "Keerthi", Department = "Development",Gender = "Female"});
    List<int> eid = new List<int>() { 1,3 };
    List<Person> SelectedEmployeeList = new List<Person>();
    var temp = eid.Select(i => 
                EmployeeList.ContainsKey(i) 
                ? EmployeeList[i]
                : null
            ).Where(i => i != null).ToList();
}

你可以这样使用

var ids = {1, 2, 3};  
var query = from item in context.items             
where ids.Contains(item.id )             
select item;

在你的情况下

string[] keys = { "key1", "key2", ... }
 var query = from key in keys             
  where ids.Contains(keys  )             
   select key ;

您可以通过映射链接您的方式EDITED我错过了一个嵌套级别，他想查询哈希集而不是整个字典

public void DoStuff(IEnumerable<string> key, int iClassId)
{
    mappings.Where(i=>key.Contains(i.Key)).ToList().ForEach(obj=>
    {
        foreach (var classEntry in
             from c in obj.Value
             where c.StartsWith(iClassId + "(")
             select c)
        {
            DoStuffWithEntry(classEntry);
        }
}

更改key参数和from c ... section。

你这样称呼它

string[] keys = new string[]{"key1", "key2", ... , "keyN"};
DoStuff(keys, 123);

应该可以

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