tOp(OpKernelConstruction* context) : OpKernel(context) {    // Get the index of the value to preserve     OP_REQUIRES_OK(context,                    context->GetAttr("preserve_index", &preserve_index));     // Check that preserve_index is positive     OP_REQUIRES(context, preserve_index >= 0,                 errors::InvalidArgument("Need preserve_index >= 0, got ",                                         preserve_index));   }    void Compute(OpKernelContext* context) override {     // Grab the input tensor     const Tensor& input_tensor = context->input(0);     auto input = input_tensor.flat<