Save predictions and validation set in a dataframe

I’ve used TabularPandas to preprocessed my data and trained a sklearn random forest regression model. Now I’d like to create a dataframe with validation data, labels and predictions.
I’ve tried to convert to.valid.show() to a dataframe in order to add the predictions as a new column, but can not find a way to convert a nontype object to a dataframe.
How can I create a dataframe with validation data set and predictions?