enable making an expression from a tensor spec

3 files changed, 26 insertions, 0 deletions

diff --git a/eval/src/tests/eval/tensor_spec/tensor_spec_test.cpp b/eval/src/tests/eval/tensor_spec/tensor_spec_test.cpp
index aa62e52f6f4..7c48606d6dd 100644
--- a/eval/src/tests/eval/tensor_spec/tensor_spec_test.cpp
+++ b/eval/src/tests/eval/tensor_spec/tensor_spec_test.cpp
@@ -19,6 +19,17 @@ TEST("require that a tensor spec can be converted to and from slime") {
     EXPECT_EQUAL(TensorSpec::from_slime(slime.get()), spec);
 }
 
+TEST("require that a tensor spec can be converted to and from an expression") {
+    TensorSpec spec("tensor<float>(x[2],y{})");
+    spec.add({{"x", 0}, {"y", "xxx"}}, 1.0)
+        .add({{"x", 0}, {"y", "yyy"}}, 2.0)
+        .add({{"x", 1}, {"y", "xxx"}}, 3.0)
+        .add({{"x", 1}, {"y", "yyy"}}, 4.0);
+    vespalib::string expr = spec.to_expr();
+    fprintf(stderr, "expr: \n%s\n", expr.c_str());
+    EXPECT_EQUAL(TensorSpec::from_expr(expr), spec);
+}
+
 TEST("require that tensor specs can be diffed") {
     TensorSpec expect("tensor(x[2],y{})");
     expect.add({{"x", 0}, {"y", "xxx"}}, 1.5)
diff --git a/eval/src/vespa/eval/eval/tensor_spec.cpp b/eval/src/vespa/eval/eval/tensor_spec.cpp
index 684242fc485..5e833710e8c 100644
--- a/eval/src/vespa/eval/eval/tensor_spec.cpp
+++ b/eval/src/vespa/eval/eval/tensor_spec.cpp
@@ -284,6 +284,20 @@ TensorSpec::to_slime(slime::Cursor &tensor) const
     }
 }
 
+vespalib::string
+TensorSpec::to_expr() const
+{
+    vespalib::string out = _type;
+    out.append(":{");
+    CommaTracker cell_list;
+    for (const auto &cell: _cells) {
+        cell_list.maybe_add_comma(out);
+        out.append(make_string("%s:%g", as_string(cell.first).c_str(), cell.second.value));
+    }
+    out.append("}");
+    return out;
+}
+
 TensorSpec
 TensorSpec::from_slime(const slime::Inspector &tensor)
 {
diff --git a/eval/src/vespa/eval/eval/tensor_spec.h b/eval/src/vespa/eval/eval/tensor_spec.h
index eab4c4ff49d..29e8a978c12 100644
--- a/eval/src/vespa/eval/eval/tensor_spec.h
+++ b/eval/src/vespa/eval/eval/tensor_spec.h
@@ -75,6 +75,7 @@ public:
     vespalib::string to_string() const;
     TensorSpec normalize() const;
     void to_slime(slime::Cursor &tensor) const;
+    vespalib::string to_expr() const;
     static TensorSpec from_slime(const slime::Inspector &tensor);
     static TensorSpec from_value(const eval::Value &value);
     static TensorSpec from_expr(const vespalib::string &expr);