public List<Long> sortedValues(Comparator<String> keyComparator) {
        final List<String> collect = data.keySet().stream().sorted(keyComparator).collect(Collectors.toList());
        List<Long> values = new ArrayList<>(collect.size());
        collect.forEach(key -> values.add(data.get(key)));
        return values;
    }
@return the sum of all values.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/metrics/DataTable.java