private static Sample[] left(List<Sample> samples, List<String> labelKeys) {
            return samples.stream().map(s -> {
                ImmutableMap<String, String> ll = ImmutableMap.<String, String>builder()
                                                              .putAll(Maps.filterKeys(s.labels,
                                                                                      key -> !labelKeys.contains(key)
                                                              ))
                                                              .build();
                return s.toBuilder().labels(ll).build();
            }).toArray(Sample[]::new);
        }
The parsing context holds key results more than sample collection.
oap-server/analyzer/meter-analyzer/src/main/java/org/apache/skywalking/oap/meter/analyzer/dsl/SampleFamily.java