Instance#

class capymoa.instance.Instance[source]#

Bases: object

An instance is a single data point in a stream. It contains a feature vector and a schema that describes the datastream it belongs to.

In supervised learning, your more likely to encounter LabeledInstance or RegressionInstance which are subclasses of Instance with a class label or target value respectively.

__init__( schema: Schema, instance: InstanceExample | ndarray[Any, dtype[float64]], ) → None[source]#

Creates a new instance.

Its recommended that you prefer using from_array() or from_java_instance() to create instances, as they provide a more user-friendly interface.

Parameters:

schema – A schema that describes the datastream the instance belongs to.
instance – A vector of features (float values) or a Java instance.

Raises:

ValueError – If the given instance type is of an unsupported type.

classmethod from_java_instance( schema: Schema, java_instance: InstanceExample, ) → Instance[source]#

classmethod from_array( schema: Schema, instance: ndarray[Any, dtype[float64]], ) → Instance[source]#

A class constructor to create an instance from a schema and a vector of features.

This is useful in the rare cases you need to create custom unlabeled instances from scratch. In most cases, your datastream will automatically create instances for you.

>>> from capymoa.stream import Schema
...
>>> from capymoa.instance import Instance
>>> import numpy as np
>>> schema = Schema.from_custom(
...     ["f1", "f2"],
...     dataset_name="CustomDataset",
...     values_for_class_label=["yes", "no"]
... )
>>> x = np.array([0.1, 0.2])
>>> instance = Instance.from_array(schema, x)
>>> instance
Instance(
    Schema(CustomDataset),
    x=ndarray(..., 2)
)

Parameters:

schema – A schema that describes the datastream the instance belongs to.
instance – A vector (numpy.ndarray) of features (float values

Returns:

A new Instance object

property schema: Schema#: Returns the schema of the instance and the stream it belongs to.

property x: ndarray[Any, dtype[float64]]#: Returns a feature vector containing float values for the instance.

property java_instance: InstanceExample#: Returns a representation of the instance in Java for use in MOA. This method is for advanced users who want to directly interact with MOA’s Java API.