title: How can I cross-validate by Pytorch and Optuna
body: <p>I want to use cross-validation against the official Optuna and pytorch-based sample code (<a href="https://github.com/optuna/optuna/blob/master/examples/pytorch_simple.py" rel="noreferrer">https://github.com/optuna/optuna/blob/master/examples/pytorch_simple.py</a>).</p>
  <p>I thought about splitting the data for cross-validation and trying parameter tuning for each fold, but it seems that the average accuracy of each parameter cannot be obtained because the parameters that can be checked in study.trials_dataframe() are different each time.</p>