Add `lod_array_length` operator

paddle/operators/lod_array_length_op.cc

+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserved.
+
+   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/framework/lod_tensor_array.h"
+#include "paddle/framework/op_registry.h"
+
+namespace paddle {
+namespace operators {
+
+class LoDArrayLengthOp : public framework::OperatorBase {
+ public:
+  LoDArrayLengthOp(const std::string &type,
+                   const framework::VariableNameMap &inputs,
+                   const framework::VariableNameMap &outputs,
+                   const framework::AttributeMap &attrs)
+      : OperatorBase(type, inputs, outputs, attrs) {}
+  void Run(const framework::Scope &scope,
+           const platform::DeviceContext &dev_ctx) const override {
+    auto &x = scope.FindVar(Input("X"))->Get<framework::LoDTensorArray>();
+    auto &out =
+        *scope.FindVar(Output("Out"))->GetMutable<framework::LoDTensor>();
+    out.Resize({1});
+    auto cpu = platform::CPUPlace();
+    *out.mutable_data<int64_t>(cpu) = static_cast<int64_t>(x.size());
+  }
+};
+
+class LoDArrayLengthProtoMaker : public framework::OpProtoAndCheckerMaker {
+ public:
+  LoDArrayLengthProtoMaker(framework::OpProto *proto,
+                           framework::OpAttrChecker *op_checker)
+      : OpProtoAndCheckerMaker(proto, op_checker) {
+    AddInput("X", "(LoDTensorArray) The input tensor array.");
+    AddOutput("Out", "(Tensor) 1x1 CPU Tensor of length, int64_t");
+    AddComment(R"DOC(Get the length of lod tensor array
+
+Out = len(X)
+
+NOTE: The output is a CPU Tensor since the control variable should be only in
+CPU and the length of LoDTensorArray should be used as control variables.
+)DOC");
+  }
+};
+
+class LoDArrayLengthInferShape : public framework::InferShapeBase {
+ public:
+  void operator()(framework::InferShapeContext *context) const override {
+    PADDLE_ENFORCE(context->HasInput("X"));
+    PADDLE_ENFORCE(context->HasOutput("Out"));
+    context->SetOutputDim("Out", {1});
+  }
+};
+
+}  // namespace operators
+}  // namespace paddle
+
+namespace ops = paddle::operators;
+REGISTER_OPERATOR(lod_array_length, ops::LoDArrayLengthOp,
+                  ops::LoDArrayLengthInferShape, ops::LoDArrayLengthProtoMaker,
+                  paddle::framework::EmptyGradOpMaker);

python/paddle/v2/framework/layers.py

@@ -941,3 +941,12 @@ def shrink_memory(x, i, table, main_program=None):
         outputs={'Out': [out]},
         attrs={})
     return out
+
+
+def array_length(array, main_program=None):
+    helper = LayerHelper('array_length', **locals())
+    tmp = helper.create_tmp_variable(dtype='int64')
+    tmp.stop_gradient = True
+    helper.append_op(
+        type='lod_array_length', inputs={'X': [array]}, outputs={'Out': [tmp]})
+    return tmp

python/paddle/v2/framework/tests/test_lod_array_length_op.py

+import unittest
+import paddle.v2.framework.layers as layers
+from paddle.v2.framework.executor import Executor
+import paddle.v2.framework.core as core
+import numpy
+
+
+class TestLoDArrayLength(unittest.TestCase):
+    def test_array_length(self):
+        tmp = layers.zeros(shape=[10], dtype='int32')
+        i = layers.fill_constant(shape=[1], dtype='int64', value=10)
+        arr = layers.array_write(tmp, i=i)
+        arr_len = layers.array_length(arr)
+        cpu = core.CPUPlace()
+        exe = Executor(cpu)
+        result = numpy.array(exe.run(fetch_list=[arr_len])[0])
+        self.assertEqual(11, result[0])
+
+
+if __name__ == '__main__':
+    unittest.main()