code: def get_values(self, data, filter_values):
          
          out = []
          for bucket in data.buckets:
              key = self.get_value(bucket)
              out.append((
                  key,
                  self.get_metric(bucket),
                  self.is_filtered(key, filter_values)
              ))
          return out
docs: Turn the raw bucket data into a list of tuples containing the key,
          number of documents and a flag indicating whether this value has been
          selected or not.