def build_string_table(measurements)
      common_tags = @registry.common_tags
      table = {}
      common_tags.each do |k, v|
        table[k] = 0
        table[v] = 0
      end
      table[:name] = 0
      measurements.each do |m|
        table[m.id.name] = 0
        m.id.tags.each do |k, v|
          table[k] = 0
          table[v] = 0
        end
      end
      keys = table.keys.sort
      keys.each_with_index do |str, index|
        table[str] = index
      end
      table
    end
def build_string_table(measurements)
      common_tags = @registry.common_tags
      table = {}
      common_tags.each do |k, v|
        table[k] = 0
        table[v] = 0
      end
      table[:name] = 0
      measurements.each do |m|
        table[m.id.name] = 0
        m.id.tags.each do |k, v|
          table[k] = 0
          table[v] = 0
        end
      end
      keys = table.keys.sort
      keys.each_with_index do |str, index|
        table[str] = index
      end
      table
    end
Build a string table from the list of measurements
 Unique words are identified, and assigned a number starting from 0 based
 on their lexicographical order