Hashtable 1

[stevenk140]

I have a hashtable and a value that matches up with a key. Is there an easy way of getting the key from the value? (Without search through all values to find the index)

Or is a SortedList better from going back for forward between keys and values?

Steven

 

[venur]

Hi,

You can get the value from the Hashtable if you know the key name without going through the loop.

Hashtable ht = new Hashtable();

ht.Add("Key1", "Value1"
ht.Add("Key2", "Value2"
ht.Add("Key3", "Value3"
ht.Add("Key4", "Value4"
ht.Add("Key5", "Value5"

Console.WriteLine(h.Item("Key3&quot);

Before that just make sure the key contins in the Hashtable.
with h.ContainsKey("Key3&quot


Cheers
Venu

 

[stevenk140]

Hello,

What if I have the value and want to get the key? (and I don't want to iterate through all values to find the matching key index)

Steven

 

[venur]

Hi,

Sorry, I read the quetion wrong.

Cheers,
Venu

 

[chiph]

stevenk140 -

In that case you would have to iterate through all the entries in your hashtable.

Have you considered reversing what you use as keys? Or maybe have two hashtables - one with the key as the key, and one with the value as the key?

Of course, depending on how many values you need to store, and how fast you need access to them, a database table might be a good solution.

Chip H.


If you want to get the best response to a question, please check out FAQ222-2244 first

 

[obislavu]

As chiph said you should implement your class with two HashTable members: one to map key->value direction and another to map value->key direction.
Implement in the new class functions like Lookup for the key->value direction and ReverseLookup for the value->key direction e.g. mainly what you want.
Your new class should be derived minimum from ICollection, and IEnumerable.
Here is a starting example:

public class MyHashtable : IDictionary, ICollection, IEnumerable
{
   private Hashtable m_htKey2Val = null;
   private Hashtable m_htVal2Key = null;
   public MyHashtable ()
  {
	m_htKey2Val = new Hashtable();
	m_htVal2Key = new Hashtable();
  }
   private MyHashtable (Hashtable ht)
	{
		m_htKey2Val = ht;
		m_htVal2Key = new Hashtable();
		foreach( object key in ht.Keys )
		{
			m_htVal2Key [ht[key]] = key;
		}
	}
public void Add( object key, object val )
	{
		m_htKey2Val.Add( key, val );
		m_.htVal2Key. Add( val, key );
	}

public void Remove( object key )
	{
		object val = m_htVal2Key [key];
		m_htKey2Val .Remove( key );
		m_htVal2Key .Remove( val );
	}
//This ReverseLookup will do the job.

public object ReverseLookup( object val )
	{
		return m_htVal2Key [val];
	}
 // .... 
}
Hashtable h1=new Hasttable();
h1.Add("k1","George");
MyHasTable hh= new MyHashtable(h1);
string s1 = (string)hh.ReverseLookup("George");

-obislavu-

 

[stevenk140]

Thats a great idea. Thank you.