Make num_top_classes parameter's default value equal to 2

client/rest-high-level/src/main/java/org/elasticsearch/client/ml/dataframe/Classification.java

@@ -48,6 +48,7 @@ public static Builder builder(String dependentVariable) {
     static final ParseField FEATURE_BAG_FRACTION = new ParseField("feature_bag_fraction");
     static final ParseField PREDICTION_FIELD_NAME = new ParseField("prediction_field_name");
     static final ParseField TRAINING_PERCENT = new ParseField("training_percent");
+    static final ParseField NUM_TOP_CLASSES = new ParseField("num_top_classes");
 
     private static final ConstructingObjectParser<Classification, Void> PARSER =
         new ConstructingObjectParser<>(
@@ -61,7 +62,8 @@ public static Builder builder(String dependentVariable) {
                 (Integer) a[4],
                 (Double) a[5],
                 (String) a[6],
-                (Double) a[7]));
+                (Double) a[7],
+                (Integer) a[8]));
 
     static {
         PARSER.declareString(ConstructingObjectParser.constructorArg(), DEPENDENT_VARIABLE);
@@ -72,6 +74,7 @@ public static Builder builder(String dependentVariable) {
         PARSER.declareDouble(ConstructingObjectParser.optionalConstructorArg(), FEATURE_BAG_FRACTION);
         PARSER.declareString(ConstructingObjectParser.optionalConstructorArg(), PREDICTION_FIELD_NAME);
         PARSER.declareDouble(ConstructingObjectParser.optionalConstructorArg(), TRAINING_PERCENT);
+        PARSER.declareInt(ConstructingObjectParser.optionalConstructorArg(), NUM_TOP_CLASSES);
     }
 
     private final String dependentVariable;
@@ -82,10 +85,11 @@ public static Builder builder(String dependentVariable) {
     private final Double featureBagFraction;
     private final String predictionFieldName;
     private final Double trainingPercent;
+    private final Integer numTopClasses;
 
     private Classification(String dependentVariable, @Nullable Double lambda, @Nullable Double gamma, @Nullable Double eta,
                            @Nullable Integer maximumNumberTrees, @Nullable Double featureBagFraction, @Nullable String predictionFieldName,
-                           @Nullable Double trainingPercent) {
+                           @Nullable Double trainingPercent, @Nullable Integer numTopClasses) {
         this.dependentVariable = Objects.requireNonNull(dependentVariable);
         this.lambda = lambda;
         this.gamma = gamma;
@@ -94,6 +98,7 @@ private Classification(String dependentVariable, @Nullable Double lambda, @Nulla
         this.featureBagFraction = featureBagFraction;
         this.predictionFieldName = predictionFieldName;
         this.trainingPercent = trainingPercent;
+        this.numTopClasses = numTopClasses;
     }
 
     @Override
@@ -133,6 +138,10 @@ public Double getTrainingPercent() {
         return trainingPercent;
     }
 
+    public Integer getNumTopClasses() {
+        return numTopClasses;
+    }
+
     @Override
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
         builder.startObject();
@@ -158,14 +167,17 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         if (trainingPercent != null) {
             builder.field(TRAINING_PERCENT.getPreferredName(), trainingPercent);
         }
+        if (numTopClasses != null) {
+            builder.field(NUM_TOP_CLASSES.getPreferredName(), numTopClasses);
+        }
         builder.endObject();
         return builder;
     }
 
     @Override
     public int hashCode() {
         return Objects.hash(dependentVariable, lambda, gamma, eta, maximumNumberTrees, featureBagFraction, predictionFieldName,
-            trainingPercent);
+            trainingPercent, numTopClasses);
     }
 
     @Override
@@ -180,7 +192,8 @@ public boolean equals(Object o) {
             && Objects.equals(maximumNumberTrees, that.maximumNumberTrees)
             && Objects.equals(featureBagFraction, that.featureBagFraction)
             && Objects.equals(predictionFieldName, that.predictionFieldName)
-            && Objects.equals(trainingPercent, that.trainingPercent);
+            && Objects.equals(trainingPercent, that.trainingPercent)
+            && Objects.equals(numTopClasses, that.numTopClasses);
     }
 
     @Override
@@ -197,6 +210,7 @@ public static class Builder {
         private Double featureBagFraction;
         private String predictionFieldName;
         private Double trainingPercent;
+        private Integer numTopClasses;
 
         private Builder(String dependentVariable) {
             this.dependentVariable = Objects.requireNonNull(dependentVariable);
@@ -237,9 +251,14 @@ public Builder setTrainingPercent(Double trainingPercent) {
             return this;
         }
 
+        public Builder setNumTopClasses(Integer numTopClasses) {
+            this.numTopClasses = numTopClasses;
+            return this;
+        }
+
         public Classification build() {
             return new Classification(dependentVariable, lambda, gamma, eta, maximumNumberTrees, featureBagFraction, predictionFieldName,
-                trainingPercent);
+                trainingPercent, numTopClasses);
         }
     }
 }

client/rest-high-level/src/test/java/org/elasticsearch/client/MachineLearningIT.java

@@ -1266,8 +1266,7 @@ public void testPutDataFrameAnalyticsConfig_GivenRegression() throws Exception {
             .setDest(DataFrameAnalyticsDest.builder()
                 .setIndex("put-test-dest-index")
                 .build())
-            .setAnalysis(org.elasticsearch.client.ml.dataframe.Regression
-                .builder("my_dependent_variable")
+            .setAnalysis(org.elasticsearch.client.ml.dataframe.Regression.builder("my_dependent_variable")
                 .setTrainingPercent(80.0)
                 .build())
             .setDescription("this is a regression")
@@ -1301,9 +1300,9 @@ public void testPutDataFrameAnalyticsConfig_GivenClassification() throws Excepti
             .setDest(DataFrameAnalyticsDest.builder()
                 .setIndex("put-test-dest-index")
                 .build())
-            .setAnalysis(org.elasticsearch.client.ml.dataframe.Classification
-                .builder("my_dependent_variable")
+            .setAnalysis(org.elasticsearch.client.ml.dataframe.Classification.builder("my_dependent_variable")
                 .setTrainingPercent(80.0)
+                .setNumTopClasses(1)
                 .build())
             .setDescription("this is a classification")
             .build();

client/rest-high-level/src/test/java/org/elasticsearch/client/documentation/MlClientDocumentationIT.java

@@ -2951,6 +2951,7 @@ public void testPutDataFrameAnalytics() throws Exception {
                 .setFeatureBagFraction(0.4) // <6>
                 .setPredictionFieldName("my_prediction_field_name") // <7>
                 .setTrainingPercent(50.0) // <8>
+                .setNumTopClasses(1) // <9>
                 .build();
             // end::put-data-frame-analytics-classification
 

client/rest-high-level/src/test/java/org/elasticsearch/client/ml/dataframe/ClassificationTests.java

@@ -34,6 +34,7 @@ public static Classification randomClassification() {
             .setFeatureBagFraction(randomBoolean() ? null : randomDoubleBetween(0.0, 1.0, false))
             .setPredictionFieldName(randomBoolean() ? null : randomAlphaOfLength(10))
             .setTrainingPercent(randomBoolean() ? null : randomDoubleBetween(1.0, 100.0, true))
+            .setNumTopClasses(randomBoolean() ? null : randomIntBetween(0, 10))
             .build();
     }
 

docs/java-rest/high-level/ml/put-data-frame-analytics.asciidoc

@@ -118,6 +118,7 @@ include-tagged::{doc-tests-file}[{api}-classification]
 <6> The fraction of features which will be used when selecting a random bag for each candidate split. A double in (0, 1].
 <7> The name of the prediction field in the results object.
 <8> The percentage of training-eligible rows to be used in training. Defaults to 100%.
+<9> The number of top classes to be reported in the results. Defaults to 2.
 
 ===== Regression
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/dataframe/analyses/Classification.java

@@ -65,6 +65,11 @@ public static Classification fromXContent(XContentParser parser, boolean ignoreU
         Stream.of(Types.categorical(), Types.discreteNumerical(), Types.bool())
             .flatMap(Set::stream)
             .collect(Collectors.toUnmodifiableSet());
+    /**
+     * As long as we only support binary classification it makes sense to always report both classes with their probabilities.
+     * This way the user can see if the prediction was made with confidence they need.
+     */
+    private static final int DEFAULT_NUM_TOP_CLASSES = 2;
 
     private final String dependentVariable;
     private final BoostedTreeParams boostedTreeParams;
@@ -86,7 +91,7 @@ public Classification(String dependentVariable,
         this.dependentVariable = ExceptionsHelper.requireNonNull(dependentVariable, DEPENDENT_VARIABLE);
         this.boostedTreeParams = ExceptionsHelper.requireNonNull(boostedTreeParams, BoostedTreeParams.NAME);
         this.predictionFieldName = predictionFieldName;
-        this.numTopClasses = numTopClasses == null ? 0 : numTopClasses;
+        this.numTopClasses = numTopClasses == null ? DEFAULT_NUM_TOP_CLASSES : numTopClasses;
         this.trainingPercent = trainingPercent == null ? 100.0 : trainingPercent;
     }
 
@@ -106,6 +111,10 @@ public String getDependentVariable() {
         return dependentVariable;
     }
 
+    public int getNumTopClasses() {
+        return numTopClasses;
+    }
+
     public double getTrainingPercent() {
         return trainingPercent;
     }

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/dataframe/analyses/ClassificationTests.java

@@ -19,6 +19,8 @@
 
 public class ClassificationTests extends AbstractSerializingTestCase<Classification> {
 
+    private static final BoostedTreeParams BOOSTED_TREE_PARAMS = new BoostedTreeParams(0.0, 0.0, 0.5, 500, 1.0);
+
     @Override
     protected Classification doParseInstance(XContentParser parser) throws IOException {
         return Classification.fromXContent(parser, false);
@@ -43,32 +45,68 @@ protected Writeable.Reader<Classification> instanceReader() {
         return Classification::new;
     }
 
-    public void testConstructor_GivenTrainingPercentIsNull() {
-        Classification classification = new Classification("foo", new BoostedTreeParams(0.0, 0.0, 0.5, 500, 1.0), "result", 3, null);
-        assertThat(classification.getTrainingPercent(), equalTo(100.0));
-    }
-
-    public void testConstructor_GivenTrainingPercentIsBoundary() {
-        Classification classification = new Classification("foo", new BoostedTreeParams(0.0, 0.0, 0.5, 500, 1.0), "result", 3, 1.0);
-        assertThat(classification.getTrainingPercent(), equalTo(1.0));
-        classification = new Classification("foo", new BoostedTreeParams(0.0, 0.0, 0.5, 500, 1.0), "result", 3, 100.0);
-        assertThat(classification.getTrainingPercent(), equalTo(100.0));
-    }
-
     public void testConstructor_GivenTrainingPercentIsLessThanOne() {
         ElasticsearchStatusException e = expectThrows(ElasticsearchStatusException.class,
-            () -> new Classification("foo", new BoostedTreeParams(0.0, 0.0, 0.5, 500, 1.0), "result", 3, 0.999));
+            () -> new Classification("foo", BOOSTED_TREE_PARAMS, "result", 3, 0.999));
 
         assertThat(e.getMessage(), equalTo("[training_percent] must be a double in [1, 100]"));
     }
 
     public void testConstructor_GivenTrainingPercentIsGreaterThan100() {
         ElasticsearchStatusException e = expectThrows(ElasticsearchStatusException.class,
-            () -> new Classification("foo", new BoostedTreeParams(0.0, 0.0, 0.5, 500, 1.0), "result", 3, 100.0001));
+            () -> new Classification("foo", BOOSTED_TREE_PARAMS, "result", 3, 100.0001));
 
         assertThat(e.getMessage(), equalTo("[training_percent] must be a double in [1, 100]"));
     }
 
+    public void testConstructor_GivenNumTopClassesIsLessThanZero() {
+        ElasticsearchStatusException e = expectThrows(ElasticsearchStatusException.class,
+            () -> new Classification("foo", BOOSTED_TREE_PARAMS, "result", -1, 1.0));
+
+        assertThat(e.getMessage(), equalTo("[num_top_classes] must be an integer in [0, 1000]"));
+    }
+
+    public void testConstructor_GivenNumTopClassesIsGreaterThan1000() {
+        ElasticsearchStatusException e = expectThrows(ElasticsearchStatusException.class,
+            () -> new Classification("foo", BOOSTED_TREE_PARAMS, "result", 1001, 1.0));
+
+        assertThat(e.getMessage(), equalTo("[num_top_classes] must be an integer in [0, 1000]"));
+    }
+
+    public void testGetNumTopClasses() {
+        Classification classification = new Classification("foo", BOOSTED_TREE_PARAMS, "result", 7, 1.0);
+        assertThat(classification.getNumTopClasses(), equalTo(7));
+
+        // Boundary condition: num_top_classes == 0
+        classification = new Classification("foo", BOOSTED_TREE_PARAMS, "result", 0, 1.0);
+        assertThat(classification.getNumTopClasses(), equalTo(0));
+
+        // Boundary condition: num_top_classes == 1000
+        classification = new Classification("foo", BOOSTED_TREE_PARAMS, "result", 1000, 1.0);
+        assertThat(classification.getNumTopClasses(), equalTo(1000));
+
+        // num_top_classes == null, default applied
+        classification = new Classification("foo", BOOSTED_TREE_PARAMS, "result", null, 1.0);
+        assertThat(classification.getNumTopClasses(), equalTo(2));
+    }
+
+    public void testGetTrainingPercent() {
+        Classification classification = new Classification("foo", BOOSTED_TREE_PARAMS, "result", 3, 50.0);
+        assertThat(classification.getTrainingPercent(), equalTo(50.0));
+
+        // Boundary condition: training_percent == 1.0
+        classification = new Classification("foo", BOOSTED_TREE_PARAMS, "result", 3, 1.0);
+        assertThat(classification.getTrainingPercent(), equalTo(1.0));
+
+        // Boundary condition: training_percent == 100.0
+        classification = new Classification("foo", BOOSTED_TREE_PARAMS, "result", 3, 100.0);
+        assertThat(classification.getTrainingPercent(), equalTo(100.0));
+
+        // training_percent == null, default applied
+        classification = new Classification("foo", BOOSTED_TREE_PARAMS, "result", 3, null);
+        assertThat(classification.getTrainingPercent(), equalTo(100.0));
+    }
+
     public void testFieldCardinalityLimitsIsNonNull() {
         assertThat(createTestInstance().getFieldCardinalityLimits(), is(not(nullValue())));
     }

x-pack/plugin/ml/qa/native-multi-node-tests/src/test/java/org/elasticsearch/xpack/ml/integration/ClassificationIT.java

@@ -83,7 +83,7 @@ public void testSingleNumericFeatureAndMixedTrainingAndNonTrainingRows() throws
             assertThat((String) resultsObject.get("keyword-field_prediction"), is(in(KEYWORD_FIELD_VALUES)));
             assertThat(resultsObject.containsKey("is_training"), is(true));
             assertThat(resultsObject.get("is_training"), is(destDoc.containsKey(KEYWORD_FIELD)));
-            assertThat(resultsObject.containsKey("top_classes"), is(false));
+            assertTopClasses(resultsObject, 2, KEYWORD_FIELD, KEYWORD_FIELD_VALUES, String::valueOf);
         }
 
         assertProgress(jobId, 100, 100, 100, 100);
@@ -120,7 +120,7 @@ public void testWithOnlyTrainingRowsAndTrainingPercentIsHundred() throws Excepti
             assertThat((String) resultsObject.get("keyword-field_prediction"), is(in(KEYWORD_FIELD_VALUES)));
             assertThat(resultsObject.containsKey("is_training"), is(true));
             assertThat(resultsObject.get("is_training"), is(true));
-            assertThat(resultsObject.containsKey("top_classes"), is(false));
+            assertTopClasses(resultsObject, 2, KEYWORD_FIELD, KEYWORD_FIELD_VALUES, String::valueOf);
         }
 
         assertProgress(jobId, 100, 100, 100, 100);

x-pack/plugin/src/test/resources/rest-api-spec/test/ml/data_frame_analytics_crud.yml

@@ -1810,7 +1810,7 @@ setup:
       "maximum_number_trees": 400,
       "feature_bag_fraction": 0.3,
       "training_percent": 60.3,
-      "num_top_classes": 0
+      "num_top_classes": 2
     }
   }}
   - is_true: create_time