static Map<String, Set<String>> getComponentHostMap(Map<String, Map<String, Set<String>>> serviceComponentHostMap) {
    return serviceComponentHostMap.values().stream()
      .reduce(StackAdvisorAdapter::mergeDisjunctMaps)
      .orElse(new HashMap<>());
  }
Extracts a [component -> hosts] map from the [service -> component -> hosts] map. Services
with empty component map will be ignored
@param serviceComponentHostMap the input map
@return the extracted map
ambari-server/src/main/java/org/apache/ambari/server/topology/addservice/StackAdvisorAdapter.java