Dictionary ทำงานในลักษณะของ key, value

1. การใช้งาน Dictionary เบื้องต้น
2. การใช้งาน Dictionary กับ foreach
3. ทดลองดึง value ด้วย TryGetValue
4. ตรวจสอบว่ามี key แล้วหรือยังด้วย ContainsKey
5. ดึงเฉพาะ value ทั้งหมดด้วย ValueCollection
6. ดึงเฉพาะ key ทั้งหมดด้วย KeyCollection

• Dictionary<TKey,TValue> Class

1.การใช้งาน Dictionary เบื้องต้น

using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, string> data 
                = new Dictionary<string, string>();

            data.Add("key1", "value1");
            data.Add("key2", "value2");

            Console.WriteLine(data["key1"]);
            Console.WriteLine(data["key2"]);

            Console.ReadKey();
        }
    }
}
// The example displays the following output:
//       value1
//       value2

2.การใช้งาน Dictionary กับ foreach

using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, string> data
                = new Dictionary<string, string>();

            data.Add("key1", "value1");
            data.Add("key2", "value2");
            foreach (string key in data.Keys)
            {
                Console.WriteLine("{0} : {1}", key, data[key]);
            }

            Console.ReadKey();
        }
    }
}
// The example displays the following output:
//      key1 : value1
//      key2 : value2

.ใช้ KeyValuePair

using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, string> data
                = new Dictionary<string, string>();

            data.Add("key1", "value1");
            data.Add("key2", "value2");

            foreach (KeyValuePair<string, string> kvp in data)
            {
                Console.WriteLine("Key = {0}, Value = {1}",
                    kvp.Key, kvp.Value);
            }

            Console.ReadKey();
        }
    }
}
// The example displays the following output:
//      Key = key1, Value = value1
//      Key = key2, Value = value2

3.ทดลองดึง value ด้วย TryGetValue

using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, string> data
                = new Dictionary<string, string>();

            data.Add("key1", "value1");
            data.Add("key2", "value2");

            string value = "";
            if (data.TryGetValue("key1", out value))
            {
                Console.WriteLine("For key = 'key1', value = {0}.", value);
            }
            else
            {
                Console.WriteLine("Key = 'key1' is not found.");
            }

            if (data.TryGetValue("key3", out value))
            {
                Console.WriteLine("For key = 'key3', value = {0}.", value);
            }
            else
            {
                Console.WriteLine("Key = 'key3' is not found.");
            }

            Console.ReadKey();
        }
    }
}
// The example displays the following output:
//      For key = 'key1', value = value1.
//      Key = 'key3' is not found.

4.ตรวจสอบว่ามี key แล้วหรือยังด้วย ContainsKey

using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, string> data
                = new Dictionary<string, string>();

            data.Add("key1", "value1");
            data.Add("key2", "value2");

            // ContainsKey can be used to test keys before inserting them.
            if (!data.ContainsKey("key4"))
            {
                data.Add("key4", "value4");
                Console.WriteLine("Value added for key = 'key4': {0}", data["key4"]);
            }

            foreach (string key in data.Keys)
            {
                Console.WriteLine("{0} : {1}", key, data[key]);
            }

            Console.ReadKey();
        }
    }
}
// The example displays the following output:
//      Value added for key = 'key4': value4
//      key1 : value1
//      key2 : value2
//      key4 : value4

5.ดึงเฉพาะ value ทั้งหมดด้วย ValueCollection

using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, string> data
                = new Dictionary<string, string>();

            data.Add("key1", "value1");
            data.Add("key2", "value2");

            // To get the values alone, use the Values property.
            Dictionary<string, string>.ValueCollection valueColl =
                data.Values;

            // The elements of the ValueCollection are strongly typed
            // with the type that was specified for dictionary values.
            Console.WriteLine();
            foreach (string s in valueColl)
            {
                Console.WriteLine("Value = {0}", s);
            }

            Console.ReadKey();
        }
    }
}
// The example displays the following output:
//      Value = value1
//      Value = value2

6.ดึงเฉพาะ key ทั้งหมดด้วย KeyCollection

using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, string> data
                = new Dictionary<string, string>();

            data.Add("key1", "value1");
            data.Add("key2", "value2");

            // To get the keys alone, use the Keys property.
            Dictionary<string, string>.KeyCollection keyColl =
                data.Keys;

            // The elements of the KeyCollection are strongly typed
            // with the type that was specified for dictionary keys.
            Console.WriteLine();
            foreach (string s in keyColl)
            {
                Console.WriteLine("Key = {0}", s);
            }

            Console.ReadKey();
        }
    }
}
// The example displays the following output:
//      Key = key1
//      Key = key2