show(quiet = false) {
        return [...this]
            .map(({ group, groupKey }) => {
                const groupLog = `--\n[${JSON.stringify(groupKey)}]\n--`;
                if (!quiet) {
                    console.log(groupLog);
                }
                return groupLog + "\n" + group.show(10, quiet);
            })
            .reduce((p, n) => p + "\n" + n);
    }
Display the GroupedDataFrame as String Table.
@param {Boolean} [quiet=false] Quiet mode. If true, it doesn't trigger console.log().
@returns {String} The GroupedDataFrame as String Table.
@example
groupedDf.show()