@staticmethod
def sanity_check_categorical(df):
    """Sanity check for 'dimensionality explosion' on categorical types
        Args:
            df (dataframe): The dataframe to check the categorical columns
        Returns:
            None
        """
    for column in df.select_dtypes(include='category').columns:
        num_unique = df[column].nunique()
        if num_unique > 20:
            print('WARNING: {:s} will expand into {:d} dimensions...'.
                format(column, num_unique))
