From b2ea86592479a78a35e58151d8f9f51a5baa300c Mon Sep 17 00:00:00 2001
From: Lester Solbakken <lesters@yahoo-inc.com>
Date: Thu, 6 Jul 2017 09:59:04 +0200
Subject: Small fixes to mapped hash join

---
 .../main/java/com/yahoo/tensor/functions/Join.java | 59 ++++++++++++++--------
 1 file changed, 37 insertions(+), 22 deletions(-)

(limited to 'vespajlib/src/main/java/com/yahoo/tensor/functions/Join.java')

diff --git a/vespajlib/src/main/java/com/yahoo/tensor/functions/Join.java b/vespajlib/src/main/java/com/yahoo/tensor/functions/Join.java
index a7aa1d66a3d..95e3c444c1b 100644
--- a/vespajlib/src/main/java/com/yahoo/tensor/functions/Join.java
+++ b/vespajlib/src/main/java/com/yahoo/tensor/functions/Join.java
@@ -12,8 +12,16 @@ import com.yahoo.tensor.TensorAddress;
 import com.yahoo.tensor.TensorType;
 import com.yahoo.tensor.evaluation.EvaluationContext;
 
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
 import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
 import java.util.function.DoubleBinaryOperator;
 
 /**
@@ -284,35 +292,44 @@ public class Join extends PrimitiveTensorFunction {
     private Tensor mappedHashJoin(Tensor a, Tensor b, TensorType joinedType) {
         TensorType commonDimensionType = commonDimensions(a, b);
         if (commonDimensionType.dimensions().isEmpty()) {
-            return mappedGeneralJoin(a, b, joinedType); // If no common dimensions, fall back to mappedGeneralJoin
+            return mappedGeneralJoin(a, b, joinedType); // fallback
         }
 
-        Tensor smallerTensor = a.size() > b.size() ? b : a;
-        Tensor largerTensor = a.size() > b.size() ? a : b;
-        a = smallerTensor;
-        b = largerTensor;
+        boolean switchTensors = a.size() > b.size();
+        if (switchTensors) {
+            Tensor temp = a;
+            a = b;
+            b = temp;
+        }
+
+        // Map dimension indexes to common and joined type
+        int[] aIndexesInCommon = mapIndexes(commonDimensionType, a.type());
+        int[] bIndexesInCommon = mapIndexes(commonDimensionType, b.type());
+        int[] aIndexesInJoined = mapIndexes(a.type(), joinedType);
+        int[] bIndexesInJoined = mapIndexes(b.type(), joinedType);
 
         // Iterate once through the smaller tensor and construct a hash map for common dimensions
         Map<TensorAddress, List<Tensor.Cell>> aCellsByCommonAddress = new HashMap<>();
         for (Iterator<Tensor.Cell> cellIterator = a.cellIterator(); cellIterator.hasNext(); ) {
-            Tensor.Cell cell = cellIterator.next();
-            TensorAddress partialCommonAddress = partialCommonAddress(cell, a.type(), commonDimensionType);
+            Tensor.Cell aCell = cellIterator.next();
+            TensorAddress partialCommonAddress = partialCommonAddress(aCell, aIndexesInCommon);
             aCellsByCommonAddress.putIfAbsent(partialCommonAddress, new ArrayList<>());
-            aCellsByCommonAddress.get(partialCommonAddress).add(cell);
+            aCellsByCommonAddress.get(partialCommonAddress).add(aCell);
         }
 
-        // Iterate once through the larger tensor and use hash map to find joinable cells
-        int[] aToIndexes = mapIndexes(a.type(), joinedType);
-        int[] bToIndexes = mapIndexes(b.type(), joinedType);
+        // Iterate once through the larger tensor and use the hash map to find joinable cells
         Tensor.Builder builder = Tensor.Builder.of(joinedType);
         for (Iterator<Tensor.Cell> cellIterator = b.cellIterator(); cellIterator.hasNext(); ) {
-            Tensor.Cell cell = cellIterator.next();
-            TensorAddress partialCommonAddress = partialCommonAddress(cell, b.type(), commonDimensionType);
+            Tensor.Cell bCell = cellIterator.next();
+            TensorAddress partialCommonAddress = partialCommonAddress(bCell, bIndexesInCommon);
             for (Tensor.Cell aCell : aCellsByCommonAddress.getOrDefault(partialCommonAddress, Collections.emptyList())) {
-                TensorAddress combinedAddress = joinAddresses(aCell.getKey(), aToIndexes,
-                        cell.getKey(), bToIndexes, joinedType);
+                TensorAddress combinedAddress = joinAddresses(aCell.getKey(), aIndexesInJoined,
+                        bCell.getKey(), bIndexesInJoined, joinedType);
                 if (combinedAddress == null) continue; // not combinable
-                builder.cell(combinedAddress, combinator.applyAsDouble(aCell.getValue(), cell.getValue()));
+                double combinedValue = switchTensors ?
+                        combinator.applyAsDouble(bCell.getValue(), aCell.getValue()) :
+                        combinator.applyAsDouble(aCell.getValue(), bCell.getValue());
+                builder.cell(combinedAddress, combinedValue);
             }
         }
 
@@ -378,13 +395,11 @@ public class Join extends PrimitiveTensorFunction {
         return typeBuilder.build();
     }
 
-    private TensorAddress partialCommonAddress(Tensor.Cell cell, TensorType type, TensorType commonDimensions) {
+    private TensorAddress partialCommonAddress(Tensor.Cell cell, int[] indexMap) {
         TensorAddress address = cell.getKey();
-        String[] labels = new String[commonDimensions.dimensions().size()];
+        String[] labels = new String[indexMap.length];
         for (int i = 0; i < labels.length; ++i) {
-            String name = commonDimensions.dimensions().get(i).name();
-            int index = type.indexOfDimension(name).orElseThrow(RuntimeException::new); // invariant, must exist
-            labels[i] = address.label(index);
+            labels[i] = address.label(indexMap[i]);
         }
         return TensorAddress.of(labels);
 
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