error occur in Inverse Document frequency(IDF) method in c#

See more:

C#

IDF( is a popular measure of a word's importance. The IDF invari- ably appears in a host of heuristic measures used in information retrieval. However, so far the IDF has itself been a heuristic.

mathamatically IDF is the

IDF(t,D)=log(Total Number documents/Number of Document matching term);
Actually i have develop one application for document clustering. in this i have

one IDF method like as

private static float FindInverseDocumentFrequency(string term)
       {
          // DocumentVector dv = new DocumentVector();

           //find the  no. of document that contains the term in whole document collection
           int count = documentCollection.ToArray().Where(s => r.Split(s.ToUpper()).ToArray().Contains(term.ToUpper())).Count();
           /*
            * log of the ratio of  total no of document in the collection to the no. of document containing the term
            * we can also use Math.Log(count/(1+documentCollection.Count)) to deal with divide by zero case;
            */
           return (float)Math.Log((float)documentCollection.Count / (float)count);

       }

this method use the following declared statments in program


documentCollection like as

documentCollection = collection.DocumentList[dv.content] as Hashtable;

DocumentList is like as

private DocumentCollection docCollection=  new DocumentCollection() { DocumentList = new Hashtable() };

s is the string like as

List<string> removeList = new List<string>(){"\"","\r","\n","(",")","[","]","{","}","","."," ",","};
            foreach (string s in removeList)
            {
                distinctTerms.Remove(s);
            }

r is the Regular expression

private static Regex r = new Regex("([ \\t{}()\",:;. \n])");

IDF method have some error like as:

"

 documentcollection.toarray() occur error like as

"'System.Collections.Hashtable' does not contain a definition for 'ToArray' and no extension method 'ToArray' accepting a first argument of type 'System.Collections.Hashtable' could be found (are you missing a using directive or an assembly reference?)

please slove this error.


please help me.thank u