如何使用LINQ篩選字典中的鍵列表

Question

我將此字典mappings聲明為Dictionary<string, HashSet<string>> 。
我也有這種方法可以對字典中的哈希集執行操作：

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
}

在一種情況下，我需要對映射字典中的多個鍵執行此操作，並且我認為最好對鍵列表進行重寫和過濾，而不是為每個鍵調用DoStuff來優化執行。

目前，我這樣做：

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

邏輯上是這樣的，而不是每個都調用DoStuff（FilterOnKeys不是方法-就是我想要的...）：

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

Answer 1

聽起來像您想要的：

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

foreach (var entry in query)
{
    ...
}

（為了便於閱讀，我個人會為查詢使用一個單獨的變量-我不太希望foreach循環的聲明位變得越來越大。）

Answer 2

我根據您的要求使用LINQ

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

完整的C＃源代碼為

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

您可以通過映射來限制自己的方式編輯我錯過了嵌套級別，他想查詢哈希集而不是整個字典

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參數，並from c ...部分更改了。

你這樣稱呼它

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

這應該工作

Answer 4

你可以使用這樣的東西

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

在你的情況下

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