Optional return types in pyg::sampler::subgraph

CHANGELOG.md

@@ -18,6 +18,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added `CMake` support ([#5](https://github.com/pyg-team/pyg-lib/pull/5))
 - Added `pyg.cuda_version()` ([#4](https://github.com/pyg-team/pyg-lib/pull/4))
 ### Changed
+- Optional return types in `pyg.subgraph()` ([#40](https://github.com/pyg-team/pyg-lib/pull/40))
 - Absolute headers ([#30](https://github.com/pyg-team/pyg-lib/pull/30))
 - Use `at::equal` rather than `at::all` in tests ([#37](https://github.com/pyg-team/pyg-lib/pull/37))
 ### Removed

pyg_lib/csrc/sampler/cpu/subgraph_kernel.cpp

@@ -9,17 +9,19 @@ namespace sampler {
 
 namespace {
 
-std::tuple<at::Tensor, at::Tensor, at::Tensor> subgraph_kernel(
+std::tuple<at::Tensor, at::Tensor, c10::optional<at::Tensor>> subgraph_kernel(
     const at::Tensor& rowptr,
     const at::Tensor& col,
-    const at::Tensor& nodes) {
+    const at::Tensor& nodes,
+    const bool return_edge_id) {
   TORCH_CHECK(rowptr.is_cpu(), "'rowptr' must be a CPU tensor");
   TORCH_CHECK(col.is_cpu(), "'col' must be a CPU tensor");
   TORCH_CHECK(nodes.is_cpu(), "'nodes' must be a CPU tensor");
 
   const auto deg = rowptr.new_empty({nodes.size(0)});
   const auto out_rowptr = rowptr.new_empty({nodes.size(0) + 1});
-  at::Tensor out_col, out_edge_id;
+  at::Tensor out_col;
+  c10::optional<at::Tensor> out_edge_id = c10::nullopt;
 
   AT_DISPATCH_INTEGRAL_TYPES(nodes.scalar_type(), "subgraph_kernel", [&] {
     const auto rowptr_data = rowptr.data_ptr<scalar_t>();
@@ -53,9 +55,12 @@ std::tuple<at::Tensor, at::Tensor, at::Tensor> subgraph_kernel(
     at::cumsum_out(tmp, deg, /*dim=*/0);
 
     out_col = col.new_empty({out_rowptr_data[nodes.size(0)]});
-    out_edge_id = col.new_empty({out_rowptr_data[nodes.size(0)]});
     auto out_col_data = out_col.data_ptr<scalar_t>();
-    auto out_edge_id_data = out_edge_id.data_ptr<scalar_t>();
+    scalar_t* out_edge_id_data;
+    if (return_edge_id) {
+      out_edge_id = col.new_empty({out_rowptr_data[nodes.size(0)]});
+      out_edge_id_data = out_edge_id.value().data_ptr<scalar_t>();
+    }
 
     // Customize `grain_size` based on the work each thread does (it will need
     // to find `col.size(0) / nodes.size(0)` neighbors on average).
@@ -72,7 +77,8 @@ std::tuple<at::Tensor, at::Tensor, at::Tensor> subgraph_kernel(
           const auto search = to_local_node.find(w);
           if (search != to_local_node.end()) {
             out_col_data[offset] = search->second;
-            out_edge_id_data[offset] = j;
+            if (return_edge_id)
+              out_edge_id_data[offset] = j;
             offset++;
           }
         }

pyg_lib/csrc/sampler/subgraph.cpp

@@ -6,10 +6,11 @@
 namespace pyg {
 namespace sampler {
 
-std::tuple<at::Tensor, at::Tensor, at::Tensor> subgraph(
+std::tuple<at::Tensor, at::Tensor, c10::optional<at::Tensor>> subgraph(
     const at::Tensor& rowptr,
     const at::Tensor& col,
-    const at::Tensor& nodes) {
+    const at::Tensor& nodes,
+    const bool return_edge_id) {
   at::TensorArg rowptr_t{rowptr, "rowtpr", 1};
   at::TensorArg col_t{col, "col", 1};
   at::TensorArg nodes_t{nodes, "nodes", 1};
@@ -21,13 +22,13 @@ std::tuple<at::Tensor, at::Tensor, at::Tensor> subgraph(
   static auto op = c10::Dispatcher::singleton()
                        .findSchemaOrThrow("pyg::subgraph", "")
                        .typed<decltype(subgraph)>();
-  return op.call(rowptr, col, nodes);
+  return op.call(rowptr, col, nodes, return_edge_id);
 }
 
 TORCH_LIBRARY_FRAGMENT(pyg, m) {
-  m.def(
-      TORCH_SELECTIVE_SCHEMA("pyg::subgraph(Tensor rowptr, Tensor col, Tensor "
-                             "nodes) -> (Tensor, Tensor, Tensor)"));
+  m.def(TORCH_SELECTIVE_SCHEMA(
+      "pyg::subgraph(Tensor rowptr, Tensor col, Tensor "
+      "nodes, bool return_edge_id) -> (Tensor, Tensor, Tensor?)"));
 }
 
 }  // namespace sampler

pyg_lib/csrc/sampler/subgraph.h

@@ -9,10 +9,11 @@ namespace sampler {
 // Returns the induced subgraph of the graph given by `(rowptr, col)`,
 // containing only the nodes in `nodes`.
 // Returns: (rowptr, col, edge_id)
-PYG_API std::tuple<at::Tensor, at::Tensor, at::Tensor> subgraph(
+PYG_API std::tuple<at::Tensor, at::Tensor, c10::optional<at::Tensor>> subgraph(
     const at::Tensor& rowptr,
     const at::Tensor& col,
-    const at::Tensor& nodes);
+    const at::Tensor& nodes,
+    const bool return_edge_id = true);
 
 }  // namespace sampler
 }  // namespace pyg

test/csrc/sampler/test_subgraph.cpp

@@ -18,5 +18,5 @@ TEST(SubgraphTest, BasicAssertions) {
   auto expected_col = at::tensor({1, 0, 2, 1, 3, 2}, options);
   EXPECT_TRUE(at::equal(std::get<1>(out), expected_col));
   auto expected_edge_id = at::tensor({3, 4, 5, 6, 7, 8}, options);
-  EXPECT_TRUE(at::equal(std::get<2>(out), expected_edge_id));
+  EXPECT_TRUE(at::equal(std::get<2>(out).value(), expected_edge_id));
 }