gistfile1.rb

# Given a set of documents this method returns a list of tags associated with
# those documents ordered by the ones occuring on the most documents. Tags th
# only appear on one doc are excluded from the list.
# If the user supplies a specific tag to exclude it will not be included
# in the list.
def related_tags(docs, exclude_tag = nil)
  # DM triggers single SQL query for all docs' tags when doc.tags is called.
  docs[0,20].inject({}) do |hash, doc|
    doc.tags.inject(hash) do |hsh, tag|
      hsh[tag] ||= 0
      hsh[tag] -= 1 unless exclude_tag == tag
      hsh
    end
  end.to_a.sort_by{|(tag, c)| c }[0, 24].map{|(tag,c)| tag }
end