docs: def statistics(cls, function, group=None):
          """
          Compute statistics (average, max, median, minimun and sum) from _results
          into a dictionary of numpy array.
          """
          benchmark = cls.results(function, group)
          results = {}
          for name, stat in {'avg': numpy.average, 'max': numpy.amax, 'med': numpy.median, 'min': numpy.amin, 'sum': numpy.sum}.items():
              results[name] = stat(benchmark, axis=0)
          return results