add api for detecting cell existence

* new API "has(TensorAddress)" detects if a Tensor has a cell with the given address.
* use new API in join and merge.  This will give different results for
  cells that are present but contain NaN versus cells that aren't present at all.
* use new API in slice. This gives a different default (0, not NaN) when trying to
  access cells that aren't present.

1 files changed, 8 insertions, 2 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/tensor/functions/Slice.java b/vespajlib/src/main/java/com/yahoo/tensor/functions/Slice.java
index 607c9a0ab44..da24aef50bc 100644
--- a/vespajlib/src/main/java/com/yahoo/tensor/functions/Slice.java
+++ b/vespajlib/src/main/java/com/yahoo/tensor/functions/Slice.java
@@ -63,8 +63,14 @@ public class Slice<NAMETYPE extends Name> extends PrimitiveTensorFunction<NAMETY
         TensorType resultType = resultType(tensor.type());
 
         PartialAddress subspaceAddress = subspaceToAddress(tensor.type(), context);
-        if (resultType.rank() == 0) // shortcut common case
-            return Tensor.from(tensor.get(subspaceAddress.asAddress(tensor.type())));
+        if (resultType.rank() == 0) { // shortcut common case
+            var key = subspaceAddress.asAddress(tensor.type());
+            if (tensor.has(key)) {
+                return Tensor.from(tensor.get(key));
+            } else {
+                return Tensor.from(0.0);
+            }
+        }
 
         Tensor.Builder b = Tensor.Builder.of(resultType);
         for (Iterator<Tensor.Cell> i = tensor.cellIterator(); i.hasNext(); ) {