如何使用 LINQ 过滤字典中的键列表

Question

我将这本字典 mappings 声明为 Dictionary<string, HashSet<string>>。
我也有这种方法可以对字典中的哈希集进行处理：

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，我需要对映射字典中的多个键执行此操作，我认为最好重写和过滤键列表，而不是为每个键调用 DoStuff 以优化执行。

目前我这样做：

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

逻辑上是这样的，而不是为每个调用 DoStuff（FilterOnKeys 不是一种方法 - 正是我想要的......）：

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

Answer 1

听起来像你想要的：

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一个单独的变量，只是为了便于阅读 - 我不太热衷于 foreach 循环的声明位变得很大。）

Answer 2

我正在根据您的要求使用 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();

}

Answer 3

你可以使用这样的东西

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

你的情况

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

Answer 4

你可以通过映射链接你的方式 已编辑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);
        }
}

更改了key 参数和from c ... 部分。

你这样称呼它

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

这应该可以工作