to_bipartite.cc

/*!
 *  Copyright 2019-2021 Contributors
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 * \file graph/transform/to_bipartite.cc
 * \brief Convert a graph to a bipartite-structured graph.
 */

#include "to_bipartite.h"

#include <dgl/base_heterograph.h>
#include <dgl/transform.h>
#include <dgl/array.h>
#include <dgl/packed_func_ext.h>
#include <dgl/immutable_graph.h>
#include <dgl/runtime/registry.h>
#include <dgl/runtime/container.h>
#include <vector>
#include <tuple>
#include <utility>
#include "../../array/cpu/array_utils.h"

namespace dgl {

using namespace dgl::runtime;
using namespace dgl::aten;

namespace transform {

namespace {

// Since partial specialization is not allowed for functions, use this as an
// intermediate for ToBlock where XPU = kDLCPU.
template<typename IdType>
std::tuple<HeteroGraphPtr, std::vector<IdArray>>
ToBlockCPU(HeteroGraphPtr graph, const std::vector<IdArray> &rhs_nodes,
    bool include_rhs_in_lhs, std::vector<IdArray>* const lhs_nodes_ptr) {
  std::vector<IdArray>& lhs_nodes = *lhs_nodes_ptr;
  const bool generate_lhs_nodes = lhs_nodes.empty();

  const int64_t num_etypes = graph->NumEdgeTypes();
  const int64_t num_ntypes = graph->NumVertexTypes();
  std::vector<EdgeArray> edge_arrays(num_etypes);

  CHECK(rhs_nodes.size() == static_cast<size_t>(num_ntypes))
    << "rhs_nodes not given for every node type";

  const std::vector<IdHashMap<IdType>> rhs_node_mappings(rhs_nodes.begin(), rhs_nodes.end());
  std::vector<IdHashMap<IdType>> lhs_node_mappings;

  if (generate_lhs_nodes) {
  // build lhs_node_mappings -- if we don't have them already
    if (include_rhs_in_lhs)
      lhs_node_mappings = rhs_node_mappings;  // copy
    else
      lhs_node_mappings.resize(num_ntypes);
  } else {
    lhs_node_mappings = std::vector<IdHashMap<IdType>>(lhs_nodes.begin(), lhs_nodes.end());
  }


  for (int64_t etype = 0; etype < num_etypes; ++etype) {
    const auto src_dst_types = graph->GetEndpointTypes(etype);
    const dgl_type_t srctype = src_dst_types.first;
    const dgl_type_t dsttype = src_dst_types.second;
    if (!aten::IsNullArray(rhs_nodes[dsttype])) {
      const EdgeArray& edges = graph->Edges(etype);
      if (generate_lhs_nodes) {
        lhs_node_mappings[srctype].Update(edges.src);
      }
      edge_arrays[etype] = edges;
    }
  }

  std::vector<int64_t> num_nodes_per_type;
  num_nodes_per_type.reserve(2 * num_ntypes);

  const auto meta_graph = graph->meta_graph();
  const EdgeArray etypes = meta_graph->Edges("eid");
  const IdArray new_dst = Add(etypes.dst, num_ntypes);
  const auto new_meta_graph = ImmutableGraph::CreateFromCOO(
      num_ntypes * 2, etypes.src, new_dst);

  for (int64_t ntype = 0; ntype < num_ntypes; ++ntype)
    num_nodes_per_type.push_back(lhs_node_mappings[ntype].Size());
  for (int64_t ntype = 0; ntype < num_ntypes; ++ntype)
    num_nodes_per_type.push_back(rhs_node_mappings[ntype].Size());

  std::vector<HeteroGraphPtr> rel_graphs;
  std::vector<IdArray> induced_edges;
  for (int64_t etype = 0; etype < num_etypes; ++etype) {
    const auto src_dst_types = graph->GetEndpointTypes(etype);
    const dgl_type_t srctype = src_dst_types.first;
    const dgl_type_t dsttype = src_dst_types.second;
    const IdHashMap<IdType> &lhs_map = lhs_node_mappings[srctype];
    const IdHashMap<IdType> &rhs_map = rhs_node_mappings[dsttype];
    if (rhs_map.Size() == 0) {
      // No rhs nodes are given for this edge type. Create an empty graph.
      rel_graphs.push_back(CreateFromCOO(
          2, lhs_map.Size(), rhs_map.Size(),
          aten::NullArray(), aten::NullArray()));
      induced_edges.push_back(aten::NullArray());
    } else {
      IdArray new_src = lhs_map.Map(edge_arrays[etype].src, -1);
      IdArray new_dst = rhs_map.Map(edge_arrays[etype].dst, -1);
      // Check whether there are unmapped IDs and raise error.
      for (int64_t i = 0; i < new_dst->shape[0]; ++i)
        CHECK_NE(new_dst.Ptr<IdType>()[i], -1)
          << "Node " << edge_arrays[etype].dst.Ptr<IdType>()[i] << " does not exist"
          << " in `rhs_nodes`. Argument `rhs_nodes` must contain all the edge"
          << " destination nodes.";
      rel_graphs.push_back(CreateFromCOO(
          2, lhs_map.Size(), rhs_map.Size(),
          new_src, new_dst));
      induced_edges.push_back(edge_arrays[etype].id);
    }
  }

  const HeteroGraphPtr new_graph = CreateHeteroGraph(
      new_meta_graph, rel_graphs, num_nodes_per_type);

  if (generate_lhs_nodes) {
    CHECK_EQ(lhs_nodes.size(), 0) << "InteralError: lhs_nodes should be empty "
        "when generating it.";
    for (const IdHashMap<IdType> &lhs_map : lhs_node_mappings)
      lhs_nodes.push_back(lhs_map.Values());
  }
  return std::make_tuple(new_graph, induced_edges);
}

}  // namespace

template<>
std::tuple<HeteroGraphPtr, std::vector<IdArray>>
ToBlock<kDLCPU, int32_t>(HeteroGraphPtr graph,
                         const std::vector<IdArray> &rhs_nodes,
                         bool include_rhs_in_lhs,
                         std::vector<IdArray>* const lhs_nodes) {
  return ToBlockCPU<int32_t>(graph, rhs_nodes, include_rhs_in_lhs, lhs_nodes);
}

template<>
std::tuple<HeteroGraphPtr, std::vector<IdArray>>
ToBlock<kDLCPU, int64_t>(HeteroGraphPtr graph,
                         const std::vector<IdArray> &rhs_nodes,
                         bool include_rhs_in_lhs,
                         std::vector<IdArray>* const lhs_nodes) {
  return ToBlockCPU<int64_t>(graph, rhs_nodes, include_rhs_in_lhs, lhs_nodes);
}

DGL_REGISTER_GLOBAL("transform._CAPI_DGLToBlock")
.set_body([] (DGLArgs args, DGLRetValue *rv) {
    const HeteroGraphRef graph_ref = args[0];
    const std::vector<IdArray> &rhs_nodes = ListValueToVector<IdArray>(args[1]);
    const bool include_rhs_in_lhs = args[2];
    std::vector<IdArray> lhs_nodes = ListValueToVector<IdArray>(args[3]);

    HeteroGraphPtr new_graph;
    std::vector<IdArray> induced_edges;

    ATEN_XPU_SWITCH_CUDA(graph_ref->Context().device_type, XPU, "ToBlock", {
      ATEN_ID_TYPE_SWITCH(graph_ref->DataType(), IdType, {
      std::tie(new_graph, induced_edges) = ToBlock<XPU, IdType>(
          graph_ref.sptr(), rhs_nodes, include_rhs_in_lhs,
          &lhs_nodes);
      });
    });

    List<Value> lhs_nodes_ref;
    for (IdArray &array : lhs_nodes)
      lhs_nodes_ref.push_back(Value(MakeValue(array)));
    List<Value> induced_edges_ref;
    for (IdArray &array : induced_edges)
      induced_edges_ref.push_back(Value(MakeValue(array)));

    List<ObjectRef> ret;
    ret.push_back(HeteroGraphRef(new_graph));
    ret.push_back(lhs_nodes_ref);
    ret.push_back(induced_edges_ref);

    *rv = ret;
  });

};  // namespace transform

};  // namespace dgl