Decomposition

Models can be trained using pgml.train on unlabeled data to identify important features within the data. To decompose a dataset into it's principal components, we can use the table or a view. Since decomposition is an unsupervised algorithm, we don't need a column that represents a label as one of the inputs to pgml.train.

Example

This example trains models on the sklearn digits dataset -- which is a copy of the test set of the UCI ML hand-written digits datasets. This demonstrates using a table with a single array feature column for principal component analysis. You could do something similar with a vector column.

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SELECT pgml.load_dataset('digits');

-- create an unlabeled table of the images for unsupervised learning
CREATE VIEW pgml.digit_vectors AS
SELECT image FROM pgml.digits;

-- view the dataset
SELECT left(image::text, 40) || ',...}' FROM pgml.digit_vectors LIMIT 10;

-- train a simple model to cluster the data
SELECT * FROM pgml.train('Handwritten Digit Components', 'decomposition', 'pgml.digit_vectors', hyperparams => '{"n_components": 3}');

-- check out the compenents
SELECT target, pgml.decompose('Handwritten Digit Components', image) AS pca
FROM pgml.digits
LIMIT 10;

Note that the input vectors have been reduced from 64 dimensions to 3, which explain nearly half of the variance across all samples.

Algorithms

All decomposition algorithms implemented by PostgresML are online versions. You may use the pgml.decompose function to decompose novel data points after the model has been trained.

Examples

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SELECT * FROM pgml.train('Handwritten Digit Clusters', algorithm => 'pca', hyperparams => '{"n_components": 10}');