truncate

        # Rational.truncate

(from ruby core)
---
    rat.truncate([ndigits])  ->  integer or rational

---

Returns `rat` truncated (toward zero) to a precision of `ndigits`
decimal digits (default: 0).

When the precision is negative, the returned value is an integer with at
least `ndigits.abs` trailing zeros.

Returns a rational when `ndigits` is positive, otherwise returns an
integer.

    Rational(3).truncate      #=> 3
    Rational(2, 3).truncate   #=> 0
    Rational(-3, 2).truncate  #=> -1

      #    decimal      -  1  2  3 . 4  5  6
      #                   ^  ^  ^  ^   ^  ^
      #   precision      -3 -2 -1  0  +1 +2

    Rational('-123.456').truncate(+1).to_f  #=> -123.4
    Rational('-123.456').truncate(-1)       #=> -120