[ML] Change outlier detection feature influence format to nested object

docs/CHANGELOG.asciidoc

@@ -44,6 +44,7 @@
 === Enhancements
 
 * Calculate total feature importance to store with model metadata. (See {ml-pull}1387[#1387].)
+* Change outlier detection feature_influence format to array with nested objects. (See {ml-pull}1475[#1475], {es-pull}62068[#62068].)
 
 === Bug Fixes
 

lib/api/CDataFrameOutliersRunner.cc

@@ -52,7 +52,9 @@ const CDataFrameAnalysisConfigReader& parameterReader() {
 
 // Output
 const std::string OUTLIER_SCORE_FIELD_NAME{"outlier_score"};
-const std::string FEATURE_INFLUENCE_FIELD_NAME_PREFIX{"feature_influence."};
+const std::string FEATURE_NAME_FIELD_NAME{"feature_name"};
+const std::string FEATURE_INFLUENCE_FIELD_NAME{"feature_influence"};
+const std::string INFLUENCE_FIELD_NAME{"influence"};
 }
 
 CDataFrameOutliersRunner::CDataFrameOutliersRunner(const CDataFrameAnalysisSpecification& spec,
@@ -93,11 +95,19 @@ void CDataFrameOutliersRunner::writeOneRow(const core::CDataFrame& frame,
     writer.StartObject();
     writer.Key(OUTLIER_SCORE_FIELD_NAME);
     writer.Double(row[scoreColumn]);
-    if (row[scoreColumn] > m_FeatureInfluenceThreshold) {
+    if (row[scoreColumn] > m_FeatureInfluenceThreshold && numberFeatureScoreColumns > 0) {
+        writer.Key(FEATURE_INFLUENCE_FIELD_NAME);
+        writer.StartArray();
+
         for (std::size_t i = 0; i < numberFeatureScoreColumns; ++i) {
-            writer.Key(FEATURE_INFLUENCE_FIELD_NAME_PREFIX + frame.columnNames()[i]);
+            writer.StartObject();
+            writer.Key(FEATURE_NAME_FIELD_NAME);
+            writer.String(frame.columnNames()[i]);
+            writer.Key(INFLUENCE_FIELD_NAME);
             writer.Double(row[beginFeatureScoreColumns + i]);
+            writer.EndObject();
         }
+        writer.EndArray();
     }
     writer.EndObject();
 }

lib/api/unittest/CDataFrameAnalyzerOutlierTest.cc

@@ -285,8 +285,7 @@ BOOST_AUTO_TEST_CASE(testRunOutlierFeatureInfluences) {
 
     TDoubleVec expectedScores;
     TDoubleVecVec expectedFeatureInfluences;
-    TStrVec expectedNames{"feature_influence.c1", "feature_influence.c2", "feature_influence.c3",
-                          "feature_influence.c4", "feature_influence.c5"};
+    TStrVec expectedNames{"c1", "c2", "c3", "c4", "c5"};
 
     TStrVec fieldNames{"c1", "c2", "c3", "c4", "c5", ".", "."};
     TStrVec fieldValues{"", "", "", "", "", "0", ""};
@@ -301,12 +300,19 @@ BOOST_AUTO_TEST_CASE(testRunOutlierFeatureInfluences) {
     auto expectedFeatureInfluence = expectedFeatureInfluences.begin();
     for (const auto& result : results.GetArray()) {
         if (result.HasMember("row_results")) {
+
             BOOST_TEST_REQUIRE(expectedFeatureInfluence !=
                                expectedFeatureInfluences.end());
-            for (std::size_t i = 0; i < 5; ++i) {
+            for (int i = 0; i < 5; ++i) {
+                BOOST_REQUIRE_EQUAL(
+                    expectedNames[i].c_str(),
+                    result["row_results"]["results"]["ml"]["feature_influence"][i]["feature_name"]
+                        .GetString());
+
                 BOOST_REQUIRE_CLOSE_ABSOLUTE(
                     (*expectedFeatureInfluence)[i],
-                    result["row_results"]["results"]["ml"][expectedNames[i]].GetDouble(),
+                    result["row_results"]["results"]["ml"]["feature_influence"][i]["influence"]
+                        .GetDouble(),
                     1e-4 * (*expectedFeatureInfluence)[i]);
             }
             ++expectedFeatureInfluence;