Stateless REST API: short forms for sparse and mixed tensors

1 files changed, 58 insertions, 3 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/tensor/serialization/JsonFormat.java b/vespajlib/src/main/java/com/yahoo/tensor/serialization/JsonFormat.java
index cb7539d8565..bebd706f815 100644
--- a/vespajlib/src/main/java/com/yahoo/tensor/serialization/JsonFormat.java
+++ b/vespajlib/src/main/java/com/yahoo/tensor/serialization/JsonFormat.java
@@ -11,12 +11,19 @@ import com.yahoo.slime.Slime;
 import com.yahoo.slime.Type;
 import com.yahoo.tensor.DimensionSizes;
 import com.yahoo.tensor.IndexedTensor;
+import com.yahoo.tensor.MappedTensor;
 import com.yahoo.tensor.MixedTensor;
 import com.yahoo.tensor.Tensor;
 import com.yahoo.tensor.TensorAddress;
 import com.yahoo.tensor.TensorType;
+import com.yahoo.tensor.functions.ConstantTensor;
+import com.yahoo.tensor.functions.Slice;
 
+import java.util.HashSet;
 import java.util.Iterator;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 /**
  * Writes tensors on the JSON format used in Vespa tensor document fields:
@@ -46,12 +53,33 @@ public class JsonFormat {
     }
 
     /** Serializes the given tensor type and value into a short-form JSON format */
-    public static byte[] encodeShortForm(IndexedTensor tensor) {
+    public static byte[] encodeShortForm(Tensor tensor) {
         Slime slime = new Slime();
         Cursor root = slime.setObject();
         root.setString("type", tensor.type().toString());
-        Cursor value = root.setArray("value");
-        encodeList(tensor, value, new long[tensor.dimensionSizes().dimensions()], 0);
+
+        // Encode as nested lists if indexed tensor
+        if (tensor instanceof IndexedTensor) {
+            IndexedTensor denseTensor = (IndexedTensor) tensor;
+            encodeList(denseTensor, root.setArray("value"), new long[denseTensor.dimensionSizes().dimensions()], 0);
+        }
+
+        // Short form for a single mapped dimension
+        else if (tensor instanceof MappedTensor && tensor.type().dimensions().size() == 1) {
+            encodeMap((MappedTensor) tensor, root.setObject("value"));
+        }
+
+        // Short form for a mixed tensor with a single mapped dimension
+        else if (tensor instanceof MixedTensor &&
+                tensor.type().dimensions().stream().filter(TensorType.Dimension::isMapped).count() == 1) {
+            encodeMapBlocks((MixedTensor) tensor, root.setObject("value"));
+        }
+
+        // No other short forms exist: default to standard cell address output
+        else {
+            encodeCells(tensor, root.setObject("value"));
+        }
+
         return com.yahoo.slime.JsonFormat.toJsonBytes(slime);
     }
 
@@ -81,6 +109,33 @@ public class JsonFormat {
         }
     }
 
+    private static void encodeMap(MappedTensor tensor, Cursor cursor) {
+        if (tensor.type().dimensions().size() > 1)
+            throw new IllegalStateException("JSON encode of mapped tensor can only contain a single dimension");
+        tensor.cells().forEach((k,v) -> cursor.setDouble(k.label(0), v));
+    }
+
+    private static void encodeMapBlocks(MixedTensor tensor, Cursor cursor) {
+        var mappedDimensions = tensor.type().dimensions().stream().filter(d -> !d.isIndexed()).collect(Collectors.toList());
+        if (mappedDimensions.size() != 1) {
+            throw new IllegalArgumentException("Should be ensured by caller");
+        }
+        String mappedDimensionName = mappedDimensions.get(0).name();
+        int mappedDimensionIndex = tensor.type().indexOfDimension(mappedDimensionName).
+                orElseThrow(() -> new IllegalStateException("Could not find mapped dimension index"));
+
+        // Find all unique indices for the mapped dimension
+        Set<String> mappedIndices = new HashSet<>();
+        tensor.cellIterator().forEachRemaining((cell) -> mappedIndices.add(cell.getKey().label(mappedDimensionIndex)));
+
+        // Slice out dense subspace of each and encode dense subspace as a list
+        for (String mappedIndex : mappedIndices) {
+            IndexedTensor denseSubspace = (IndexedTensor) new Slice<>(new ConstantTensor<>(tensor),
+                    List.of(new Slice.DimensionValue<>(mappedDimensionName, mappedIndex))).evaluate();
+            encodeList(denseSubspace, cursor.setArray(mappedIndex), new long[denseSubspace.dimensionSizes().dimensions()], 0);
+        }
+    }
+
     /** Deserializes the given tensor from JSON format */
     // NOTE: This must be kept in sync with com.yahoo.document.json.readers.TensorReader in the document module
     public static Tensor decode(TensorType type, byte[] jsonTensorValue) {