message: Fix Reduce Mean error for MobileNets DNN
  Fix for index error for Reduce Mean
  Correct Reduce Mean indexing error
diff: @@ -494,14 +494,17 @@ void ONNXImporter::handleNode(const opencv_onnx::NodeProto& node_proto_)
  MatShape inpShape = outShapes[node_proto.input(0)];
  DictValue axes = layerParams.get("axes");
  bool keepdims = layerParams.get<int>("keepdims");
  - MatShape targetShape = inpShape;
  + MatShape targetShape;
  + std::vector<bool> shouldDelete(inpShape.size(), false);
  for (int i = 0; i < axes.size(); i++) {
  int axis = clamp(axes.get<int>(i), inpShape.size());
  - if (keepdims) {
  - targetShape[axis] = 1;
  - } else {
  - targetShape.erase(targetShape.begin() + axis);
  + shouldDelete[axis] = true;
  }
  + for (int axis = 0; axis < inpShape.size(); ++axis){
  + if (!shouldDelete[axis])
  + targetShape.push_back(inpShape[axis]);
  + else if (keepdims)
  + targetShape.push_back(1);
  }
  if (inpShape.size() == 3 && axes.size() <= 2)
  