code: public T getQuantile(final double fraction) {
      if ((fraction < 0.0) || (fraction > 1.0)) {
        throw new SketchesArgumentException("Fraction cannot be less than zero or greater than 1.0");
      }
      if      (fraction == 0.0) { return minValue_; }
      else if (fraction == 1.0) { return maxValue_; }
      else {
        final ItemsAuxiliary<T> aux = constructAuxiliary();
        return aux.getQuantile(fraction);
      }
    }
docs: This returns an approximation to the value of the data item
  that would be preceded by the given fraction of a hypothetical sorted
  version of the input stream so far.
  
  <p>We note that this method has a fairly large overhead (microseconds instead of nanoseconds)
  so it should not be called multiple times to get different quantiles from the same
  sketch. Instead use getQuantiles(). which pays the overhead only once.
  
  @param fraction the specified fractional position in the hypothetical sorted stream.
  These are also called normalized ranks or fractional ranks.
  If fraction = 0.0, the true minimum value of the stream is returned.
  If fraction = 1.0, the true maximum value of the stream is returned.
  
  @return the approximation to the value at the above fraction