public static <T> Collector<T, ?, Optional<Double>> regrInterceptDouble(ToDoubleFunction<? super T> functionX, ToDoubleFunction<? super T> functionY) {
        return collectingAndThen(
            collectors(
                regrAvgYDouble(functionX, functionY),
                regrSlopeDouble(functionX, functionY),
                regrAvgXDouble(functionX, functionY)
            ),
            t -> mapAll(t, (v1, v2, v3) -> v1 - v2 * v3)
        );
    }
Get a {@link Collector} that calculates the <code>REGR_INTERCEPT()</code> function.
jOOL-java-8/src/main/java/org/jooq/lambda/Agg.java