_apply_func(self, *args, out_dict: dict = None):
        &#34;&#34;&#34;Apply functions in out_dict to combined args dict

        Optionally logs output Subkeys and values as params and metrics using
        `mlflow.tracking` if this Vset has a `_tracking_dir`.

        Parameters
        ----------
        *args: dict
            Takes multiple dicts and combines them into one.
            Then runs vfuncs on each item in combined dict.
        out_dict: dict (optional), default None
            The dicti