コード例 #1
0
ファイル: Cluster.java プロジェクト: ashish0038/rahasia
  @Commit
  @SuppressWarnings("unused")
  private void afterDeserialization() throws Exception {
    if (otherAttributesForSerialization != null) {
      attributes.putAll(SimpleXmlWrappers.unwrap(otherAttributesForSerialization));
    }

    phrasesView = Collections.unmodifiableList(phrases);
    subclustersView = Collections.unmodifiableList(subclusters);
    // Documents will be restored on the ProcessingResult level
  }
コード例 #2
0
ファイル: ProcessingResult.java プロジェクト: renodim/carrot2
  /**
   * Creates a {@link ProcessingResult} with the provided <code>attributes</code>. Assigns unique
   * document identifiers if documents are present in the <code>attributes</code> map (under the key
   * {@link AttributeNames#DOCUMENTS}).
   */
  @SuppressWarnings("unchecked")
  ProcessingResult(Map<String, Object> attributes) {
    this.attributes = attributes;

    // Replace a modifiable collection of documents with an unmodifiable one
    final List<Document> documents = (List<Document>) attributes.get(AttributeNames.DOCUMENTS);
    if (documents != null) {
      Document.assignDocumentIds(documents);
      attributes.put(AttributeNames.DOCUMENTS, Collections.unmodifiableList(documents));
    }

    // Replace a modifiable collection of clusters with an unmodifiable one
    final List<Cluster> clusters = (List<Cluster>) attributes.get(AttributeNames.CLUSTERS);
    if (clusters != null) {
      Cluster.assignClusterIds(clusters);
      attributes.put(AttributeNames.CLUSTERS, Collections.unmodifiableList(clusters));
    }

    // Store a reference to attributes as an unmodifiable map
    this.attributesView = Collections.unmodifiableMap(attributes);
  }
コード例 #3
0
ファイル: ProcessingResult.java プロジェクト: renodim/carrot2
  /** Transfers document and cluster lists to the attributes map after deserialization. */
  @Commit
  private void afterDeserialization() throws Exception {
    if (otherAttributesForSerialization != null) {
      attributes = SimpleXmlWrappers.unwrap(otherAttributesForSerialization);
    }

    attributesView = Collections.unmodifiableMap(attributes);

    attributes.put(AttributeNames.QUERY, query != null ? query.trim() : null);
    attributes.put(AttributeNames.DOCUMENTS, documents);
    attributes.put(AttributeNames.CLUSTERS, clusters);

    // Convert document ids to the actual references
    if (clusters != null && documents != null) {
      final Map<String, Document> documentsById = Maps.newHashMap();
      for (Document document : documents) {
        documentsById.put(document.getStringId(), document);
      }

      for (Cluster cluster : clusters) {
        documentIdToReference(cluster, documentsById);
      }
    }
  }
コード例 #4
0
ファイル: Cluster.java プロジェクト: ashish0038/rahasia
/**
 * A cluster (group) of {@link Document}s. Each cluster has a human-readable label consisting of one
 * or more phrases, a list of documents it contains and a list of its subclusters. Optionally,
 * additional attributes can be associated with a cluster, e.g. {@link #OTHER_TOPICS}. This class is
 * <strong>not</strong> thread-safe.
 */
@Root(name = "group", strict = false)
@JsonAutoDetect(JsonMethod.NONE)
@JsonWriteNullProperties(false)
public final class Cluster {
  /**
   * Indicates that the cluster is an <i>Other Topics</i> cluster. Such a cluster contains documents
   * that remain unclustered at given level of cluster hierarchy.
   *
   * <p>Type of this attribute is {@link Boolean}.
   *
   * @see #setAttribute(String, Object)
   * @see #getAttribute(String)
   */
  public static final String OTHER_TOPICS = "other-topics";

  /** Default label for the <i>Other Topics</i> cluster. */
  static final String OTHER_TOPICS_LABEL = "Other Topics";

  /**
   * Score of this cluster that indicates the clustering algorithm's beliefs on the quality of this
   * cluster. The exact semantics of the score varies across algorithms.
   *
   * <p>Type of this attribute is {@link Double}.
   *
   * @see #setAttribute(String, Object)
   * @see #getAttribute(String)
   */
  public static final String SCORE = "score";

  /** @see #getId() */
  @Attribute(required = false)
  Integer id;

  /** Phrases describing this cluster. */
  @ElementList(required = false, name = "title", entry = "phrase")
  private ArrayList<String> phrases = new ArrayList<String>();

  /** A read-only list of phrases exposed in {@link #getPhrases()}. */
  private List<String> phrasesView = Collections.unmodifiableList(phrases);

  /** Subclusters of this cluster. */
  @ElementList(required = false, inline = true)
  private ArrayList<Cluster> subclusters = new ArrayList<Cluster>();

  /** A read-only list of subclusters exposed in {@link #getSubclusters()}. */
  private List<Cluster> subclustersView = Collections.unmodifiableList(subclusters);

  /** Documents contained in this cluster. */
  private final ArrayList<Document> documents = new ArrayList<Document>();

  /** A read-only list of this cluster's document exposed in {@link #getDocuments()}. */
  private final List<Document> documentsView = Collections.unmodifiableList(documents);

  /** Attributes of this cluster. */
  private Map<String, Object> attributes = new HashMap<String, Object>();

  /** A Read-only view of the attributes of this cluster. */
  private Map<String, Object> attributesView = Collections.unmodifiableMap(attributes);

  /** Cached concatenated label */
  private String labelCache = null;

  /** Cached list of documents from this cluster and subclusters */
  private List<Document> allDocuments;

  /** Attributes of this cluster for serialization/ deserialization purposes. */
  @ElementMap(entry = "attribute", key = "key", attribute = true, inline = true, required = false)
  private HashMap<String, SimpleXmlWrapperValue> otherAttributesForSerialization;

  /** List of document ids used for serialization/ deserialization purposes. */
  @ElementList(required = false, inline = true)
  List<DocumentRefid> documentIds;

  /** A helper class for serialization/ deserialization of documents with refids. */
  @Root(name = "document")
  static class DocumentRefid {
    @Attribute Integer refid;

    DocumentRefid() {}

    DocumentRefid(Integer refid) {
      this.refid = refid;
    }
  }

  /** Creates a {@link Cluster} with an empty label, no documents and no subclusters. */
  public Cluster() {}

  /**
   * Creates a {@link Cluster} with the provided <code>phrase</code> to be used as the cluster's
   * label and <code>documents</code> contained in the cluster.
   *
   * @param phrase the phrase to form the cluster's label
   * @param documents documents contained in the cluster
   */
  public Cluster(String phrase, Document... documents) {
    addPhrases(phrase);
    addDocuments(documents);
  }

  /**
   * Formats this cluster's label. If there is more than one phrase describing this cluster, phrases
   * will be separated by a comma followed by a space, e.g. "Phrase one, Phrase two". To format
   * multi-phrase label in a different way, use {@link #getPhrases()}.
   *
   * @return formatted label of this cluster
   */
  public String getLabel() {
    if (labelCache == null) {
      labelCache = StringUtils.toString(phrases, ", ");
    }
    return labelCache;
  }

  /**
   * Returns all phrases describing this cluster. The returned list is unmodifiable.
   *
   * @return phrases describing this cluster
   */
  @JsonProperty
  public List<String> getPhrases() {
    return phrasesView;
  }

  /**
   * Returns all subclusters of this cluster. The returned list is unmodifiable.
   *
   * @return subclusters of this cluster
   */
  public List<Cluster> getSubclusters() {
    return subclustersView;
  }

  /** For JSON serialization only. */
  @JsonProperty("clusters")
  @SuppressWarnings("unused")
  private List<Cluster> getSubclustersForSerialization() {
    return subclustersView.isEmpty() ? null : subclustersView;
  }

  /**
   * Returns all documents contained in this cluster. The returned list is unmodifiable.
   *
   * @return documents contained in this cluster
   */
  public List<Document> getDocuments() {
    return documentsView;
  }

  /**
   * Returns all documents contained in this cluster and (recursively) all documents from this
   * cluster's subclusters. The returned list contains unique documents, i.e. if a document is
   * attached to multiple subclusters if this cluster, the document will appear only once on the
   * list. The documents are enumerated in breadth first order, i.e. first come documents returned
   * by {@link #getDocuments()} and then documents from subclusters.
   *
   * @return all documents from this cluster and its subclusters
   */
  public List<Document> getAllDocuments() {
    if (allDocuments == null) {
      allDocuments =
          new ArrayList<Document>(collectAllDocuments(this, new LinkedHashSet<Document>()));
    }

    return allDocuments;
  }

  /**
   * Returns all documents in this cluster ordered according to the provided comparator. See {@link
   * Document} for common comparators, e.g. {@link Document#BY_ID_COMPARATOR} .
   */
  public List<Document> getAllDocuments(Comparator<Document> comparator) {
    final List<Document> sortedDocuments = Lists.newArrayList(getAllDocuments());
    Collections.sort(sortedDocuments, comparator);
    return sortedDocuments;
  }

  /** A recursive routine for collecting unique documents from this cluster and subclusters. */
  private static Set<Document> collectAllDocuments(Cluster cluster, Set<Document> docs) {
    if (cluster == null) {
      return docs;
    }

    docs.addAll(cluster.getDocuments());

    final List<Cluster> subclusters = cluster.getSubclusters();
    for (final Cluster subcluster : subclusters) {
      collectAllDocuments(subcluster, docs);
    }

    return docs;
  }

  /**
   * Adds phrases to the description of this cluster.
   *
   * @param phrases to be added to the description of this cluster
   * @return this cluster for convenience
   */
  public Cluster addPhrases(String... phrases) {
    labelCache = null;
    for (final String phrase : phrases) {
      this.phrases.add(phrase);
    }

    return this;
  }

  /**
   * Adds phrases to the description of this cluster.
   *
   * @param phrases to be added to the description of this cluster
   * @return this cluster for convenience
   */
  public Cluster addPhrases(Iterable<String> phrases) {
    labelCache = null;
    for (final String phrase : phrases) {
      this.phrases.add(phrase);
    }

    return this;
  }

  /**
   * Adds document to this cluster.
   *
   * @param documents to be added to this cluster
   * @return this cluster for convenience
   */
  public Cluster addDocuments(Document... documents) {
    for (final Document document : documents) {
      this.documents.add(document);
    }
    allDocuments = null;

    return this;
  }

  /**
   * Adds document to this cluster.
   *
   * @param documents to be added to this cluster
   * @return this cluster for convenience
   */
  public Cluster addDocuments(Iterable<Document> documents) {
    for (final Document document : documents) {
      this.documents.add(document);
    }
    allDocuments = null;

    return this;
  }

  /**
   * Adds subclusters to this cluster
   *
   * @param subclusters to be added to this cluster
   * @return this cluster for convenience
   */
  public Cluster addSubclusters(Cluster... subclusters) {
    for (final Cluster cluster : subclusters) {
      this.subclusters.add(cluster);
    }
    allDocuments = null;

    return this;
  }

  /**
   * Adds subclusters to this cluster
   *
   * @param clusters to be added to this cluster
   * @return this cluster for convenience
   */
  public Cluster addSubclusters(Iterable<Cluster> clusters) {
    for (final Cluster cluster : clusters) {
      this.subclusters.add(cluster);
    }
    allDocuments = null;

    return this;
  }

  /** Returns this cluster's {@value #SCORE} field. */
  @JsonProperty
  @Attribute(required = false)
  public Double getScore() {
    return getAttribute(SCORE);
  }

  /**
   * Sets this cluster's {@link #SCORE} field.
   *
   * @param score score to set
   * @return this cluster for convenience
   */
  @Attribute(required = false)
  public Cluster setScore(Double score) {
    return setAttribute(SCORE, score);
  }

  /**
   * Returns the attribute associated with this cluster under the provided <code>key</code>. If
   * there is no attribute under the provided <code>key</code>, <code>null</code> will be returned.
   *
   * @param key of the attribute
   * @return attribute value of <code>null</code>
   */
  @SuppressWarnings("unchecked")
  public <T> T getAttribute(String key) {
    return (T) attributes.get(key);
  }

  /**
   * Associates an attribute with this cluster.
   *
   * @param key for the attribute
   * @param value for the attribute
   * @return this cluster for convenience
   */
  public <T> Cluster setAttribute(String key, T value) {
    synchronized (attributes) {
      attributes.put(key, value);
    }
    return this;
  }

  /**
   * Returns all attributes of this cluster. The returned map is unmodifiable.
   *
   * @return all attributes of this cluster
   */
  public Map<String, Object> getAttributes() {
    return attributesView;
  }

  /**
   * Returns the size of the cluster calculated as the number of unique documents it contains,
   * including its subclusters.
   *
   * @return size of the cluster
   */
  public int size() {
    return getAllDocuments().size();
  }

  /** For serialization only. */
  @JsonProperty
  @Attribute(required = false)
  @SuppressWarnings("unused")
  private int getSize() {
    return size();
  }

  /** Empty implementation, SimpleXML requires both a getter and a setter. */
  @Attribute(required = false)
  @SuppressWarnings("unused")
  private void setSize(int size) {
    // We only serialize the size, hence empty implementation
  }

  /**
   * Internal identifier of this cluster within the {@link ProcessingResult}. This identifier is
   * assigned dynamically after clusters are passed to {@link ProcessingResult}.
   *
   * @see ProcessingResult
   */
  @JsonProperty
  public Integer getId() {
    return id;
  }

  /** Returns <code>true</code> if this cluster is the {@link #OTHER_TOPICS} cluster. */
  public boolean isOtherTopics() {
    final Boolean otherTopics = getAttribute(OTHER_TOPICS);
    return otherTopics != null && otherTopics.booleanValue();
  }

  /**
   * Sets the {@link #OTHER_TOPICS} attribute of this cluster.
   *
   * @param isOtherTopics if <code>true</code>, this cluster will be marked as an <i>Other
   *     Topics</i> cluster.
   * @return this cluster for convenience
   */
  public Cluster setOtherTopics(boolean isOtherTopics) {
    return setAttribute(OTHER_TOPICS, isOtherTopics).setScore(0.0);
  }

  /**
   * Compares clusters by size as returned by {@link #size()}. Clusters with more documents are
   * larger.
   */
  public static final Comparator<Cluster> BY_SIZE_COMPARATOR =
      Ordering.natural()
          .nullsFirst()
          .onResultOf(
              new Function<Cluster, Integer>() {
                public Integer apply(Cluster cluster) {
                  return cluster.size();
                }
              });

  /**
   * Compares clusters by score as returned by {@link #SCORE}. Clusters with larger score are
   * larger.
   */
  public static final Comparator<Cluster> BY_SCORE_COMPARATOR =
      Ordering.natural()
          .nullsFirst()
          .onResultOf(
              new Function<Cluster, Double>() {
                public Double apply(Cluster cluster) {
                  return cluster.getAttribute(SCORE);
                }
              });

  /** Compares clusters by the natural order of their labels as returned by {@link #getLabel()}. */
  public static final Comparator<Cluster> BY_LABEL_COMPARATOR =
      Ordering.natural()
          .nullsFirst()
          .onResultOf(
              new Function<Cluster, String>() {
                public String apply(Cluster cluster) {
                  return cluster.getLabel();
                }
              });

  /**
   * Compares clusters first by their size as returned by {@link #size()} and labels as returned by
   * {@link #getLabel()}. In case of equal sizes, natural order of the labels decides.
   *
   * <p><b>Please note</b>: this is a reversed comparator, so "larger" clusters end up nearer the
   * beginning of the list being sorted (which is usually the order in which the applications want
   * to display clusters).
   */
  public static final Comparator<Cluster> BY_REVERSED_SIZE_AND_LABEL_COMPARATOR =
      Ordering.from(Collections.reverseOrder(BY_SIZE_COMPARATOR)).compound(BY_LABEL_COMPARATOR);

  /**
   * Compares clusters first by their size as returned by {@link #SCORE} and labels as returned by
   * {@link #getLabel()}. In case of equal scores, natural order of the labels decides.
   *
   * <p><b>Please note</b>: this is a reversed comparator, so "larger" clusters end up nearer the
   * beginning of the list being sorted (which is usually the order in which the applications want
   * to display clusters).
   */
  public static final Comparator<Cluster> BY_REVERSED_SCORE_AND_LABEL_COMPARATOR =
      Ordering.from(Collections.reverseOrder(BY_SCORE_COMPARATOR)).compound(BY_LABEL_COMPARATOR);

  /**
   * Returns a comparator that compares clusters based on the aggregation of their size and score.
   * If <code>scoreWeight</code> is 0.0, the order depends only on cluster sizes. If <code>
   * scoreWeight</code> is 1.1, the order depends only on cluster scores. For <code>scoreWeight
   * </code> values between 0.0 and 1.0, the higher the <code>scoreWeight</code>, the more
   * contribution of cluster scores to the order. In case of a tie on the aggregated cluster size
   * and score, clusters are compared by the natural order of their labels.
   *
   * <p><b>Please note</b>: this is a reversed comparator, so "larger" clusters end up nearer the
   * beginning of the list being sorted (which is usually the order in which the applications want
   * to display clusters).
   */
  public static Comparator<Cluster> byReversedWeightedScoreAndSizeComparator(
      final double scoreWeight) {
    if (scoreWeight < 0 || scoreWeight > 1) {
      throw new IllegalArgumentException(
          "Score weight must be between 0.0 (inclusive) and 1.0 (inclusive) ");
    }

    return Ordering.natural()
        .onResultOf(
            new Function<Cluster, Double>() {
              public Double apply(Cluster cluster) {
                return -Math.pow(cluster.size(), (1 - scoreWeight))
                    * Math.pow((Double) cluster.getAttribute(SCORE), scoreWeight);
              }
            })
        .compound(BY_LABEL_COMPARATOR);
  }

  /**
   * A comparator that puts {@link #OTHER_TOPICS} clusters at the end of the list. In other words,
   * to this comparator an {@link #OTHER_TOPICS} topics cluster is "bigger" than a non-{{@link
   * #OTHER_TOPICS} cluster.
   *
   * <p><strong>Note:</strong> This comparator is designed for use in combination with other
   * comparators, such as {@link #BY_REVERSED_SIZE_AND_LABEL_COMPARATOR}. If you only need to
   * partition a list of clusters into regular and other topic ones, this is better done in linear
   * time without resorting to {@link Collections#sort(List)}.
   */
  public static final Comparator<Cluster> OTHER_TOPICS_AT_THE_END =
      Ordering.natural()
          .onResultOf(
              new Function<Cluster, Double>() {
                public Double apply(Cluster cluster) {
                  return cluster.isOtherTopics() ? 1.0 : -1.0;
                }
              });

  /**
   * Assigns sequential identifiers to the provided <code>clusters</code> (and their sub-clusters).
   * If a cluster already has an identifier, the identifier will not be changed.
   *
   * @param clusters Clusters to assign identifiers to.
   * @throws IllegalArgumentException if the provided clusters contain non-unique identifiers
   */
  public static void assignClusterIds(Collection<Cluster> clusters) {
    final ArrayList<Cluster> flattened = Lists.newArrayListWithExpectedSize(clusters.size());

    flatten(flattened, clusters);

    synchronized (clusters) {
      final HashSet<Integer> ids = Sets.newHashSet();

      // First, find the start value for the id and check uniqueness of the ids
      // already provided.
      int maxId = Integer.MIN_VALUE;
      for (final Cluster cluster : flattened) {
        if (cluster.id != null) {
          if (!ids.add(cluster.id)) {
            throw new IllegalArgumentException("Non-unique cluster id found: " + cluster.id);
          }
          maxId = Math.max(maxId, cluster.id);
        }
      }

      // We'd rather start with 0
      maxId = Math.max(maxId, -1);

      // Assign missing ids
      for (final Cluster c : flattened) {
        if (c.id == null) {
          c.id = ++maxId;
        }
      }
    }
  }

  /*
   * Recursive descent into subclusters.
   */
  private static void flatten(ArrayList<Cluster> flattened, Collection<Cluster> clusters) {
    for (Cluster c : clusters) {
      flattened.add(c);
      final List<Cluster> subclusters = c.getSubclusters();
      if (!subclusters.isEmpty()) {
        flatten(flattened, subclusters);
      }
    }
  }

  /**
   * Locate the first cluster that has id equal to <code>id</code>. The search includes all the
   * clusters in the input and their sub-clusters. The first cluster with matching identifier is
   * returned or <code>null</code> if no such cluster could be found.
   */
  public static Cluster find(int id, Collection<Cluster> clusters) {
    for (Cluster c : clusters) {
      if (c != null) {
        if (c.id != null && c.id == id) {
          return c;
        }

        if (!c.getSubclusters().isEmpty()) {
          final Cluster sub = find(id, c.getSubclusters());
          if (sub != null) {
            return sub;
          }
        }
      }
    }

    return null;
  }

  /**
   * Builds an "Other Topics" cluster that groups those documents from <code>allDocument</code> that
   * were not referenced in any cluster in <code>clusters</code>.
   *
   * @param allDocuments all documents to check against
   * @param clusters list of clusters with assigned documents
   * @return the "Other Topics" cluster
   */
  public static Cluster buildOtherTopics(List<Document> allDocuments, List<Cluster> clusters) {
    return buildOtherTopics(allDocuments, clusters, OTHER_TOPICS_LABEL);
  }

  /**
   * Builds an "Other Topics" cluster that groups those documents from <code>allDocument</code> that
   * were not referenced in any cluster in <code>clusters</code>.
   *
   * @param allDocuments all documents to check against
   * @param clusters list of clusters with assigned documents
   * @param label label for the "Other Topics" group
   * @return the "Other Topics" cluster
   */
  public static Cluster buildOtherTopics(
      List<Document> allDocuments, List<Cluster> clusters, String label) {
    final Set<Document> unclusteredDocuments = Sets.newLinkedHashSet(allDocuments);
    final Set<Document> assignedDocuments = Sets.newHashSet();

    for (Cluster cluster : clusters) {
      collectAllDocuments(cluster, assignedDocuments);
    }

    unclusteredDocuments.removeAll(assignedDocuments);

    final Cluster otherTopics = new Cluster(label);
    otherTopics.addDocuments(unclusteredDocuments);
    otherTopics.setOtherTopics(true);

    return otherTopics;
  }

  /**
   * If there are unclustered documents, appends the "Other Topics" group to the <code>clusters
   * </code>.
   *
   * @see #buildOtherTopics(List, List)
   */
  public static void appendOtherTopics(List<Document> allDocuments, List<Cluster> clusters) {
    appendOtherTopics(allDocuments, clusters, OTHER_TOPICS_LABEL);
  }

  /**
   * If there are unclustered documents, appends the "Other Topics" group to the <code>clusters
   * </code>.
   *
   * @see #buildOtherTopics(List, List, String)
   */
  public static void appendOtherTopics(
      List<Document> allDocuments, List<Cluster> clusters, String label) {
    final Cluster otherTopics = buildOtherTopics(allDocuments, clusters, label);
    if (!otherTopics.getDocuments().isEmpty()) {
      clusters.add(otherTopics);
    }
  }

  @Persist
  @SuppressWarnings("unused")
  private void beforeSerialization() {
    documentIds =
        Lists.transform(
            documents,
            new Function<Document, DocumentRefid>() {
              public DocumentRefid apply(Document document) {
                return new DocumentRefid(document.getId());
              }
            });

    // Remove score from attributes for serialization
    otherAttributesForSerialization = MapUtils.asHashMap(SimpleXmlWrappers.wrap(attributes));
    otherAttributesForSerialization.remove(SCORE);
    if (otherAttributesForSerialization.isEmpty()) {
      otherAttributesForSerialization = null;
    }
  }

  @Commit
  @SuppressWarnings("unused")
  private void afterDeserialization() throws Exception {
    if (otherAttributesForSerialization != null) {
      attributes.putAll(SimpleXmlWrappers.unwrap(otherAttributesForSerialization));
    }

    phrasesView = Collections.unmodifiableList(phrases);
    subclustersView = Collections.unmodifiableList(subclusters);
    // Documents will be restored on the ProcessingResult level
  }

  /** For JSON serialization only. */
  @JsonProperty("documents")
  @SuppressWarnings("unused")
  private List<Integer> getDocumentIds() {
    return Lists.transform(documents, Document.DocumentToId.INSTANCE);
  }

  /** For JSON and XML serialization only. */
  @JsonProperty("attributes")
  @SuppressWarnings("unused")
  private Map<String, Object> getOtherAttributes() {
    final Map<String, Object> otherAttributes = Maps.newHashMap(attributesView);
    return otherAttributes.isEmpty() ? null : otherAttributes;
  }
}
コード例 #5
0
ファイル: Cluster.java プロジェクト: ashish0038/rahasia
 /**
  * Returns all documents in this cluster ordered according to the provided comparator. See {@link
  * Document} for common comparators, e.g. {@link Document#BY_ID_COMPARATOR} .
  */
 public List<Document> getAllDocuments(Comparator<Document> comparator) {
   final List<Document> sortedDocuments = Lists.newArrayList(getAllDocuments());
   Collections.sort(sortedDocuments, comparator);
   return sortedDocuments;
 }