从字典中检索值的最快方法

Question

I have a var myDictionary = new Dictionary<int, string> with the following data:

123, "Do this"
234, "Do that"
345, "Do something"
123, "Do that"
567, "Do anything"
234, "Do something"

What's the best way for me to retrieve only the values for any given key? Say, I want to get only the values for 123.

Answer 1

If you want to have multiple different values grouped under one key you probably have to change the structure of your dictionary to something like this:

var myDictionary = new Dictionary<int, List<string>>();

You then initialize the list for each new key or if the key's already there you add the item to the list.

if (!myDictionary.ContainsKey(myKey))
{
    myDictionary[myKey] = new List<string();
}
myDictionary[myKey].Add(myItem);

And you get the items in a standard way:

if (myDictionary.ContainsKey(myKey))
{
    var results = myDictionary[myKey];
}

This will give you a list that you can then query to see what items have been returned.

Answer 2

A Dictionary object cannot have multiple items with the same key. Instead, you want to use KeyValuePair .

The code might look something like this:

var items = new List<KeyValuePair<int, String>>();

items.Add(new KeyValuePair<int, String>(123, "Do this"));
items.Add(new KeyValuePair<int, String>(234, "Do that"));
items.Add(new KeyValuePair<int, String>(345, "Do something"));
items.Add(new KeyValuePair<int, String>(123, "Do that"));
items.Add(new KeyValuePair<int, String>(567, "Do anything"));
items.Add(new KeyValuePair<int, String>(234, "Do something"));

// This is the key you are looking for
int desiredValue = 123;

foreach (var v in items.Where(kvp => kvp.Key == desiredValue))
{
    // Access the values you need here
    Console.WriteLine(v.Value);
}

Where the output would be:

Do this 
Do that

You can see this example in action here . Happy coding :)

Answer 3

See code below

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;

namespace ConsoleApplication61
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<int, List<string>> dict = new Dictionary<int, List<string>>() {
               {123, new List<string>() {"Do this", "Do that"}},
               {234, new List<string>() {"Do that", "Do something"}},
               {345, new List<string>() {"Do something"}},
               {567, new List<string>() {"Do anything"}}
            };

            List<string> results = dict[123];

        }

    }
}