Dear Karl, Thank you for taking your time in my problem.
We don't really know what your problem is. Explaining that rathern than the solution you have thought of might render a couple of alternate solutions. Perhaps something could be precalculated and stored in the documents. Perhaps feature selection (reduction) of the terms might do the trick for you. And so on.
Here is the description of my problem : I have a corpus of documents indexed with different fields. Approximately each document indexed has an average of 30 fields. Each field has about 100 terms. Normally, the hit will return less than 100 documents. For each of the 30 fields of the documents, I have to calculate the top 35 keywords from all the documents as well as the top 30 popular keywords (the keywords that are distributed in many documents - something like docFreq or IDF). And time is critical in my case as it is an interactive system. Users cannot wait long to get the results. Please let me know if you are still have some more questions. Thank in advance for your time and help. Best regards, Sengly
