units (dict of str to str or None, optional) – Physical unit for any column, keyed by column name. When a column has a
unit its header cell is suffixed with [unit] (e.g.
energy_mae[eV/atom]). Columns absent from the mapping keep a plain
header.
Returns:
A multi-line string with a header, an underline rule and one line per
row. Returns "(noresults)" when there are no rows.
