Hashtable: It's a really nice thing. It's useless. I'll try it again.

I used this item when I used to analyze the data. At that time, I even called it a few times. Today, some friends asked me about this and I would like to add some more.

System. collections. hashtable is a container used to represent a group of key/value structures. It may be called map or dictionary in other languages, and the key in its structure is used for quick search, it may be more appropriate to call a dictionary.

Hashtable does not have many methods and attributes. Most of them can also be regarded as justice, but hashtable provides the hashtable [akey] method to reference its contained objects, however, there is no index pointing to the number. That is to say, we are used to arrays. We cannot use hashtable [0] or other methods to retrieve its content, we cannot use it either.

For (INT I = 0; I
{

Console. writeline ("key -- {0}; Value -- {1}.", hashtable [I]. Key, hashtable [I]. value );

}

This code block is used to traverse data. However, if we add key-value pairs to hashtable, in many cases, we will eventually traverse the key-value pairs. How can this problem be solved? The following code will answer this question.

Foreach (dictionaryentry de in hashtable)

{

Console. writeline ("key -- {0}; Value -- {1}.", De. Key, De. value );

}

However, if you are still accustomed to using index for access, system. Collections. Specialized. namevaluecollection is a class that can be accessed using index. It is uncomfortable that its key/value must be of the string data type.

Remember that system. Collections. Specialized. listdictionary is a one-way linked list structure. Therefore, if there are not many key/value pairs, it is more efficient than hashtable.

System. Collections. Specialized. stringdictionary, the key is a case-sensitive string data type.

Hashtable hash = new hashtable ();

For (INT I = 0; I <ID. length; I ++)

{

If (ID [I]. Trim ()! = "")

{

String builid = ID [I];

String buildept = G. getxxxx (builid). Rows [0] ["XXXX"]. tostring (). Trim ();

If (! Hash. Contains (buildept ))

{

Hash. Add (buildept, builid );

}

Else

{

Hash [buildept] = (string) hash [buildept] + "," + builid;

}


}

}

Foreach (dictionaryentry de in hash)

{

String dept = de. Key. tostring (). Trim ();

String IDs = de. value. tostring (). Trim ();

}