To iterate the list in HashTable

Question

1.00/5 (1 vote)

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Hi

I have used hashtable for the following scenario.

100 Sam
100 John

Since hash table key is unqiue we cannot add 100 again . So i used a list as follows .

C#

List<string> List = new List<string>();
list.add(sam)
list.add(John)

hashtable ht = new Hashtable()
ht.add(100,list)

Now how do I iterate & display the values in output as shown?

100 Sam
John

Thanks in advance

Posted 9-Feb-12 0:55am

Vinodh.B

Updated 9-Feb-12 14:52pm

Sergey Alexandrovich Kryukov

v2

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Comments

Sergey Alexandrovich Kryukov 9-Feb-12 20:53pm

Fixed few typo and code formatting (but not code bugs).
--SA

2 solutions

Solution 2

You should never use Hashtable or any other non-generic collections in new development. They are superseded by a set of generic types as early as of .NET Framework v.2.0, when generics were introduced. Non-generic non-specialized collections are bad due to a need for type casts.

Choose from System.Collection.Generic.Dictionary, System.Collection.Generic.SortedDictionary or System.Collection.Generic.SortedList; they differ mostly in different trade-off between redundancy and performance.

Please see http://msdn.microsoft.com/en-us/library/system.collections.generic.aspx[^].

You problem will look like this:

C#

using IntIndexedStringDictionary = Dictionary<int, string>;
using Pair = KeyValuePair<int, string>;

//...

IntIndexedStringDictionary dictionary = new IntIndexedStringDictionary();
dictionary.Add(1, "first");
dictionary.Add(3, "third");
//...

foreach (Pair pair in dictionary) {
    int key = pair.Key;
    string value = pair.Value;
    //...
}

—SA

Posted 9-Feb-12 15:04pm

Sergey Alexandrovich Kryukov

Updated 9-Feb-12 15:28pm

v5

Comments

ProEnggSoft 9-Feb-12 21:22pm

Using the Generic Dictionary class is the best solution in my view too, so I voted 5.

Sergey Alexandrovich Kryukov 9-Feb-12 21:26pm

Thank you,
--SA

Tanzy123 9-Feb-12 23:43pm

helpfull ans.. +5

Sergey Alexandrovich Kryukov 10-Feb-12 0:07am

Thank you,
--SA

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Fredrik Bornander · Accepted Answer · 2012-02-09T01:20:00

Solution 1

You could do it like this;

C#

IList<string> list = new List<string>();
list.Add("Sam");
list.Add("John");

Hashtable ht = new Hashtable();
ht.Add(100, list);

foreach (object key in ht.Keys)
{
    Console.Write("{0} ", key);
    foreach (string name in (IList<string>)ht[key])
    {
        Console.WriteLine(name);
    }
}

Although I recommend using IDictionary and Dictionary from System.Collection.Generic instead of hashtable.

Hope this helps,
Fredrik

Posted 9-Feb-12 1:20am

Fredrik Bornander

Comments

santhosh-padamatinti 9-Feb-12 7:47am

Usually i uses List and dictionary only. Could you please tell me when exactly we have to use Hash table.

Fredrik Bornander 9-Feb-12 8:05am

I think the internal implementation of Dictionary is a hash table. The Dictionary is a generic class that gives you type safety when you want it and allows you to ignore it when you dont (new Dictionary<object, object>()), also because of no boxing unboxing it should be faster as well. But for me, the typesafety argument coupled with the fact that you don't have to cast all the time makes Dictionary far more attractive to use.