func dateWrapper(vals []Value, enh *EvalNodeHelper, f func(time.Time) float64) Vector {
	if len(vals) == 0 {
		return append(enh.out,
			Sample{
				Metric: labels.Labels{},
				Point:  Point{V: f(time.Unix(enh.ts/1000, 0).UTC())},
			})
	}

	for _, el := range vals[0].(Vector) {
		t := time.Unix(int64(el.V), 0).UTC()
		enh.out = append(enh.out, Sample{
			Metric: enh.dropMetricName(el.Metric),
			Point:  Point{V: f(t)},
		})
	}
	return enh.out
}
func dateWrapper(vals []Value, enh *EvalNodeHelper, f func(time.Time) float64) Vector {
	if len(vals) == 0 {
		return append(enh.out,
			Sample{
				Metric: labels.Labels{},
				Point:  Point{V: f(time.Unix(enh.ts/1000, 0).UTC())},
			})
	}

	for _, el := range vals[0].(Vector) {
		t := time.Unix(int64(el.V), 0).UTC()
		enh.out = append(enh.out, Sample{
			Metric: enh.dropMetricName(el.Metric),
			Point:  Point{V: f(t)},
		})
	}
	return enh.out
}
// Common code for date related functions.