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SPDX-FileCopyrightText: 1998-2026 Paulo Moura <pmoura@logtalk.org>
SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License");
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`nearest_centroid_classifier`
==================

Nearest Centroid classifier. Assigns to an instance the class of the
training samples whose mean (centroid) is closest to the instance.

The library implements the `classifier_protocol` defined in the
`classification_protocols` library. It provides predicates for learning a
classifier from a dataset, using it to make predictions, and exporting
it as a list of predicate clauses or to a file.

Datasets are represented as objects implementing the `dataset_protocol`
protocol from the `classification_protocols` library. See `test_files` directory
for examples.


API documentation
-----------------

Open the [../../docs/library_index.html#nearest_centroid_classifier](../../docs/library_index.html#nearest_centroid_classifier)
link in a web browser.


Loading
-------

To load this library, load the `loader.lgt` file:

	| ?- logtalk_load(nearest_centroid_classifier(loader)).


Testing
-------

To test this library predicates, load the `tester.lgt` file:

	| ?- logtalk_load(nearest_centroid_classifier(tester)).


Features
--------

- **Multiple Distance Metrics**: Euclidean, Manhattan, cosine
- **Mixed Features**: Automatically handles categorical and continuous features
- **Configurable Option**: distance metric via predicate options
- **Probability Estimation**: Provides confidence scores for predictions
- **Classifier Export**: Learned classifiers can be exported as predicate clauses


Usage
-----

### Learning a Classifier

    % Learn from a dataset object with default options (euclidean distance)
    | ?- nearest_centroid_classifier::learn(my_dataset, Classifier).
    ...

    % Learn with custom options
    | ?- nearest_centroid_classifier::learn(my_dataset, Classifier, [distance_metric(manhattan)]).
    ...

### Making Predictions

    % Predict class for a new instance
    | ?- Instance = [attr1-value1, attr2-value2, ...],
         nearest_centroid_classifier::learn(my_dataset, Classifier),
         nearest_centroid_classifier::predict(Classifier, Instance, PredictedClass).
    PredictedClass = ...
    ...

    % Predict with custom options
    | ?- nearest_centroid_classifier::predict(Classifier, Instance, PredictedClass, [distance_metric(cosine)]).
    ...

    % Get probability distribution
    | ?- nearest_centroid_classifier::predict_probabilities(Classifier, Instance, Probabilities).
    Probabilities = [class1-0.67, class2-0.33]
    ...

### Exporting the Classifier

Learned classifiers can be exported as a list of clauses or to a file for later use.

    % Export as predicate clauses
    | ?- nearest_centroid_classifier::learn(my_dataset, Classifier),
         nearest_centroid_classifier::export_to_clauses(my_dataset, Classifier, my_classifier, Clauses).
    Clauses = [my_classifier(...)]
    ...

    % Export to a file
    | ?- nearest_centroid_classifier::learn(my_dataset, Classifier),
         nearest_centroid_classifier::export_to_file(my_dataset, Classifier, my_classifier, 'classifier.pl').
    ...

### Using a learned classifier

Learned and saved classifiers can later be used for predictions without needing
to access the original training dataset.

    % Later, load the file and use the classifier
    | ?- consult('classifier.pl'),
         my_classifier(AttributeNames, FeatureTypes, Centroids),
         Instance = [...],
         nearest_centroid_classifier::predict(my_classifier(AttributeNames, FeatureTypes, Centroids), Instance, Class).
    Class = ...
    ...


Options
-------

The following options can be passed to the `predict/4` and
`predict_probabilities/4` predicates:

- `distance_metric(Metric)`: Distance metric to use. Options: `euclidean` (default), `manhattan`, `cosine`


Classifier representation
-------------------------

The learned classifier is represented as a compound term:

    nc_classifier(AttributeNames, FeatureTypes, Centroids)

Where:

- `AttributeNames`: List of attribute names in order
- `FeatureTypes`: List of types (`numeric` or `categorical`)
- `Centroids`: List of computed `Class-Centroid` pairs

When exported using `export_to_clauses/4` or `export_to_file/4`,
this classifier term is serialized directly as the single argument of the
generated predicate clause so that the exported model can be loaded and
reused as-is.


References
----------

1. Manning, Raghavan & Schütze (2008) - "Introduction to Information Retrieval". Cambridge University Press.
2. Tibshirani, Hastie, Narasimhan & Chu (2002) - "Diagnosis of multiple cancer types by shrunken centroids of gene expression". Proceedings of the National Academy of Sciences, 99(10), 6567-6572.
3. Hastie, Tibshirani & Friedman (2009) - "The Elements of Statistical Learning: Data Mining, Inference, and Prediction" (2nd Edition). Springer.
