:: DeveloperApi :: Abstract class for ML attributes.
:: DeveloperApi :: Attributes that describe a vector ML column.
:: DeveloperApi :: An enum-like type for attribute types: AttributeType$#Numeric, AttributeType$#Nominal, and AttributeType$#Binary.
:: DeveloperApi :: A binary attribute.
:: DeveloperApi :: A nominal attribute.
:: DeveloperApi :: A numeric attribute with optional summary statistics.
:: DeveloperApi ::
:: DeveloperApi :: Factory methods to create attribute groups.
:: DeveloperApi :: Factory methods for binary attributes.
:: DeveloperApi :: Factory methods for nominal attributes.
:: DeveloperApi :: Factory methods for numeric attributes.
:: DeveloperApi :: An unresolved attribute.
ML attributes
The ML pipeline API uses DataFrames as ML datasets. Each dataset consists of typed columns, e.g., string, double, vector, etc. However, knowing only the column type may not be sufficient to handle the data properly. For instance, a double column with values 0.0, 1.0, 2.0, ... may represent some label indices, which cannot be treated as numeric values in ML algorithms, and, for another instance, we may want to know the names and types of features stored in a vector column. ML attributes are used to provide additional information to describe columns in a dataset.
ML columns
A column with ML attributes attached is called an ML column. The data in ML columns are stored as double values, i.e., an ML column is either a scalar column of double values or a vector column. Columns of other types must be encoded into ML columns using transformers. We use Attribute to describe a scalar ML column, and AttributeGroup to describe a vector ML column. ML attributes are stored in the metadata field of the column schema.