sequence_erase_op.cc

/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.

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. */

#include "paddle/operators/sequence_erase_op.h"

namespace paddle {
namespace operators {

class SequenceEraseOp : public framework::OperatorWithKernel {
 public:
  using framework::OperatorWithKernel::OperatorWithKernel;

  void InferShape(framework::InferShapeContext* ctx) const override {
    PADDLE_ENFORCE(ctx->HasInput("X"),
                   "Input(X) of SequenceEraseOp should not be null.");
    PADDLE_ENFORCE(ctx->HasOutput("Out"),
                   "Output(Out) of SequenceEraseOp should not be null.");
    auto x_dims = ctx->GetInputDim("X");
    PADDLE_ENFORCE(x_dims.size() == 2 && x_dims[1] == 1,
                   "Input(X) of SequenceEraseOp should be a 2-D LoDTensor "
                   "with the 2nd dimension equal to 1.");
    ctx->SetOutputDim("Out", x_dims);
  }
};

class SequenceEraseOpMaker : public framework::OpProtoAndCheckerMaker {
 public:
  SequenceEraseOpMaker(OpProto* proto, OpAttrChecker* op_checker)
      : OpProtoAndCheckerMaker(proto, op_checker) {
    AddInput("X",
             "(2-D LoDTensor with the 2nd dim. equal to 1) "
             "Input LoDTensor of SequenceEraseOp.");
    AddOutput("Out",
              "(2-D LoDTensor with the 2nd dim. equal to 1) "
              "Output LoDTensor of SequenceEraseOp.");
    AddAttr<std::vector<int>>("tokens",
                              "(vector<int>) Tokens need to be erased from "
                              "input sequences.");
    AddComment(R"DOC(
Sequence Erase Operator.

Sequence erase operator erases tokens specified by Attr(tokens) from the input 
sequences Input(X), and outputs the remaining data and modifies the LoD 
information at the same time. For example, given a 2-D LoDTensor

    X = [[2, 2, 6, 1, 3, 9, 6, 1, 0, 1]]^T

with lod = [[0, 3, 6, 10]], there are three sequences in the input:
   
     X1 = [[2, 2, 6]]^T, X2 = [[1, 3, 9]]^T and X3 = [[6, 1, 0, 1]]^T.

If the tokens to be erased are Attr(tokens) = [2, 3, 5], after the erasing 
operation, the three sequences become

    X1' = [[6]]^T, X2' = [[1, 9]]^T and X3' = [[6, 1, 0, 1]]^T.

Hence the LoDTensor Output(Out) should be

    Out = [[6, 1, 9, 6, 1, 0, 1]]^T,

with lod = [[0, 1, 3, 7]].

An example usage for this operator is to remove the special tokens when 
computing the edit distance between two strings, such as blank, start token, 
and end token.
)DOC");
  }
};

}  // namespace operators
}  // namespace paddle

namespace ops = paddle::operators;
REGISTER_OP_WITHOUT_GRADIENT(sequence_erase, ops::SequenceEraseOp,
                             ops::SequenceEraseOpMaker);
REGISTER_OP_CPU_KERNEL(
    sequence_erase,
    ops::SequenceEraseKernel<paddle::platform::CPUDeviceContext, int32_t>);