PostgreSQL samples to a feature tensor

// Replace these public placeholders and configure example-postgres-password privately.
import aner.db;
import aner.db.postgres;
import aner.secrets;
import aner.data;
import aner.tensor;

let connection: DBConnection = postgres.connect(
    host: "postgres.example.invalid", port: 5432, database: "example_science",
    user: "example_reader", password: secrets.stored("example-postgres-password"),
    sslmode: "verify-full", timeout_seconds: 10);
// Run examples/fixtures/db_mock.sql once with your database administration tool.
// SQL and parameters travel separately; never interpolate user input into SQL.
let result: DBResult = db.query(connection,
    "SELECT sample_id, feature_a, feature_b, feature_c, label FROM aner_demo.samples WHERE label = $1::integer ORDER BY sample_id",
    List("2"), max_rows: 1000, max_bytes: 1048576);
print(db.rows(result));
if db.rows(result) > 0 {
    let table: DataTable = db.to_table(result, 1048576);
    print(data.integer(table, 0, "label"));
}
// Select numeric features in SQL to use data.to_tensor with no string/null columns.
let features = db.query(connection,
    "SELECT feature_a, feature_b, feature_c FROM aner_demo.samples ORDER BY sample_id",
    List(), max_rows: 1000, max_bytes: 1048576);
let matrix = data.to_tensor(db.to_table(features, 1048576), 1048576);
print(tensor.rows(matrix));
print(tensor.cols(matrix));
db.close(connection);