Fix clusters with single candidates. Closes #2152.

main/src/com/google/refine/clustering/binning/BinningClusterer.java

@@ -242,6 +242,7 @@ public class BinningClusterer extends Clusterer {
     public List<List<ClusteredEntry>> getJsonRepresentation() {
         EntriesComparator c = new EntriesComparator();
         return _clusters.stream()
+        		.filter(m -> m.size() > 1)
                 .map(m -> m.entrySet().stream()
                         .sorted(c)
                         .map(e -> new ClusteredEntry(e.getKey(), e.getValue()))

main/tests/server/src/com/google/refine/clustering/binning/BinningClustererTests.java

@@ -26,7 +26,10 @@
  ******************************************************************************/
 package com.google.refine.clustering.binning;
 
+import static org.testng.Assert.assertEquals;
+
 import java.io.IOException;
+import java.util.Arrays;
 
 import org.testng.annotations.Test;
 
@@ -83,4 +86,16 @@ public class BinningClustererTests extends RefineTest {
         clusterer.computeClusters(new Engine(project));
         TestUtils.isSerializedTo(clusterer, clustererJson);
     }
+    
+    @Test
+    public void testNoLonelyClusters() throws JsonParseException, JsonMappingException, IOException {
+    	Project project = createCSVProject("column\n"
+                + "c\n"
+                + "ĉ\n"
+                + "d\n");
+    	BinningClustererConfig config = ParsingUtilities.mapper.readValue(configJson, BinningClustererConfig.class);
+    	BinningClusterer clusterer = config.apply(project);
+        clusterer.computeClusters(new Engine(project));
+        assertEquals(clusterer.getJsonRepresentation().size(), 1);
+    }
 }

main/tests/server/src/com/google/refine/clustering/knn/kNNClustererTests.java

@@ -26,6 +26,8 @@
  ******************************************************************************/
 package com.google.refine.clustering.knn;
 
+import static org.testng.Assert.assertTrue;
+
 import java.io.IOException;
 
 import org.testng.annotations.Test;
@@ -72,4 +74,16 @@ public class kNNClustererTests extends RefineTest {
         
         TestUtils.isSerializedTo(clusterer, clustererJson);
     }
+    
+    @Test
+    public void testNoLonelyclusters() throws JsonParseException, JsonMappingException, IOException {
+    	Project project = createCSVProject("column\n"
+                + "foo\n"
+                + "bar\n");
+    	kNNClustererConfig config = ParsingUtilities.mapper.readValue(configJson, kNNClustererConfig.class);
+    	kNNClusterer clusterer = config.apply(project);
+    	clusterer.computeClusters(new Engine(project));
+    	
+    	assertTrue(clusterer.getJsonRepresentation().isEmpty());
+    }
 }