Determine Top Keywords from the fetched list of documents

We will be displaying the Top Keywords given by the user for report purposes sir

For example:

The user entered:

  • Donald Trump
  • Border
  • Mexico

Among these keywords, we'll be using the query_string query, to look up from the documents (articles) in our index and then display it to the user...

Now, sooner or later the user will have a lot of keywords and we would like to give a report feature to display which among his/her keywords is the one appearing the most from the fetched articles