Now, it is time to explore the data. There are many questions that we can ask, such as the following:

• What target features would we like to model supporting our goals?
• What are the useful training features for each target feature?
• Which features are not good for modeling since they leak information about target features (see the previous section)?
• Which features are not useful (for example, constant features, or features containing lot of missing values)?
• How to clean up data? What to do with missing values? Can we engineer new features?