preprocessing operations
- common operations for the three groups of data (training/validation/test data)
- nan_inf_imputer
- specific operations for the three groups of data
- normalization (usually, normalization on validation/test data is performed with the parameters saved from the similar operations on training data)
preprocessing steps
- doing the common operations on the training/validation/test data
- doing the specific operations on training data, and save the parameters for latter use
- with the save parameters, doing specific operations on validation and test data
- train the model with training and validation data
- testing the model with test data
