for _, a := range as {
			if !a.Value.isEmptyGroup() {
				as2 = append(as2, a)
			}
		}
		as = as2
	}
	return Value{num: uint64(len(as)), any: groupptr(unsafe.SliceData(as))}
}

// countEmptyGroups returns the number of empty group values in its argument.
func countEmptyGroups(as []Attr) int {
	n := 0
	for _, a := range as {
		if a.Value.isEmptyGroup() {
			n++
		}
	}
	return n
}