Compute statistics (average, max, median, minimun and sum) from _results
        into a dictionary of numpy array.

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