Return values in a format amenable to printing in a table.

def _get_rpt_fmt(fld, val, itemid2name=None):
        """Return values in a format amenable to printing in a table."""
        if fld.startswith("ratio_"):
            return "{N}/{TOT}".format(N=val[0], TOT=val[1])
        elif fld in set(['study_items', 'pop_items', 'alt_ids']):
            if itemid2name is not None:
                val = [itemid2name.get(v, v) for v in val]
            return ", ".join([str(v) for v in sorted(val)])
        return val