reduceRight(func, init) {
        return typeof init === "undefined"
            ? this[__rows__].reduceRight((p, n) => func(p, n))
            : this[__rows__].reduceRight((p, n) => func(p, n), init);
    }
Reduce DataFrame into a value, starting from the last row (see .reduce()).
@param {Function} func The reduce function taking 2 parameters, previous and next.
@param [init] The initial value of the reducer.
@returns A reduced value.
@example
df.reduceRight((p, n) => p > n ? p : n, 0)