[feature] document frequency count functions and broadcasting

Closes #2 (closed)

Implements to functions to calculate the document frequency

• ExtractWords is a FlatMap to map sentences to words per vertex
• this can then be grouped by words
• CountDocumentFrequencyis a groupReduce function to count the amount of documents a word occurs.

---

SimilarityMeasurerWithDocumentFrequencyBroadcast gets the broadcasted variable and sets it to TFIDFSimilarityComponent.

The Linker should calculate the DocumentFrequency and broadcast it to the DOCUMENT_FREQUENCY_BROADCAST variable.

    Map<String, Integer> wordsInDoc =
      benchmarkDataCollection.getVertices().flatMap(new WordExtractor(sourceAttribute, tokenizer))
        .groupBy(1)
        .reduceGroup(new CountDocumentFrequency())
        .collect().stream().collect(Collectors.toMap(t1 -> t1.f0, t2 -> t2.f1)); // could be implemented better

      // ....
      blockedVertices.flatMap(new SimilarityMeasurerWithDocumentFrequencyBroadcast(similarityComponents))
        .withBroadcastSet(getExecutionEnvironment().fromElements(wordsInDoc),
          TFIDFSimilarityComponent.DOCUMENT_FREQUENCY_BROADCAST);

---

Also changed TFIDF to use the pre calculated documentsFrequency

Also Closes #5 (closed)

src/main/java/org/gradoop/famer/linking/similarityMeasuring/dataStructures/TFIDFSimilarityComponent.java

@@ -3,18 +3,31 @@ package org.gradoop.famer.linking.similarityMeasuring.dataStructures;
 import org.gradoop.famer.linking.similarityMeasuring.methods.SimilarityComputation;
 import org.gradoop.famer.linking.similarityMeasuring.methods.TFIDF;
 
+import java.util.Map;
+
 public class TFIDFSimilarityComponent extends SimilarityComponent {
+
+    public static final String DOCUMENT_FREQUENCY_BROADCAST = "documentFrequency";
+    private final String tokenizer;
+    private Map<String, Integer> documentFrequency;
+
     /**
      * Creates an instance of TFIDFSimilarityComponent
      *
      * @param baseConfig The base configuration for the similarity component
+     * @param tokenizer  Word tokenizer
      */
-    public TFIDFSimilarityComponent(SimilarityComponentBaseConfig baseConfig) {
+    public TFIDFSimilarityComponent(SimilarityComponentBaseConfig baseConfig, String tokenizer) {
         super(baseConfig);
+        this.tokenizer = tokenizer;
     }
 
     @Override
     public SimilarityComputation<String> buildSimilarityComputation() throws Exception {
-        return new TFIDF();
+        return new TFIDF(this.documentFrequency, tokenizer);
+    }
+
+    public void setDocumentFrequency(Map<String, Integer> documentFrequency) {
+        this.documentFrequency = documentFrequency;
     }
 }