kmeans 2.0.2

Small and fast library for k-means clustering calculations.
Documentation 
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use crate::memory::*;

/// Enum with possible abort strategies.
/// These strategies specify when a running iteration (with the k-means calculation) is aborted.
pub enum AbortStrategy<T: Primitive> {
    /// This strategy aborts the calculation directly after an iteration produced no improvement where `improvement > threshold`
    /// for the first time.
    /// ## Fields:
    /// - **threshold**: Threshold, used to detect an improvement (`improvement > threshold`)
    NoImprovement { threshold: T },
    /// This strategy aborts the calculation, when there have not been any improvements after **x** iterations,
    /// where `improvement > threshold`.
    /// ## Fields:
    /// - **x**: The amount of consecutive without improvement, after which the calculation is aborted
    /// - **threshold**: Threshold, used to detect an improvement (`improvement > threshold`)
    /// - **abort_on_negative**: Specifies whether the strategy instantly aborts when a negative improvement occured (**true**), or if
    ///   negative improvements are handled as "no improvements" (**false**).
    NoImprovementForXIterations { x: usize, threshold: T, abort_on_negative: bool },
}
impl<T: Primitive> AbortStrategy<T> {
    pub(crate) fn create_logic(&self) -> Box<dyn AbortStrategyLogic<T>> {
        match *self {
            AbortStrategy::NoImprovementForXIterations {
                x,
                threshold,
                abort_on_negative,
            } => Box::new(NoImprovementForXIterationsLogic {
                x,
                threshold,
                abort_on_negative,
                prev_error: T::infinity(),
                no_improvement_counter: 0,
            }),
            AbortStrategy::NoImprovement { threshold } => Box::new(NoImprovementLogic {
                threshold,
                prev_error: T::infinity(),
            }),
        }
    }
}

pub(crate) trait AbortStrategyLogic<T: Primitive> {
    /// Function that has to be called once an iteration of the calculation ended, a new error was calculated.
    /// ## Arguments
    /// - **error**: The new **error (distsum), after an iteration
    /// ## Returns
    /// - **true** if the calculation should continue
    /// - **false** if the calculation should abort
    fn next(&mut self, error: T) -> bool;
}

pub(crate) struct NoImprovementLogic<T: Primitive> {
    threshold: T,
    prev_error: T,
}
impl<T: Primitive> AbortStrategyLogic<T> for NoImprovementLogic<T> {
    fn next(&mut self, error: T) -> bool {
        let improvement = self.prev_error - error;
        self.prev_error = error;
        improvement > self.threshold
    }
}

pub(crate) struct NoImprovementForXIterationsLogic<T: Primitive> {
    x: usize,
    threshold: T,
    abort_on_negative: bool,
    prev_error: T,
    no_improvement_counter: usize,
}
impl<T: Primitive> AbortStrategyLogic<T> for NoImprovementForXIterationsLogic<T> {
    fn next(&mut self, error: T) -> bool {
        let improvement = self.prev_error - error;
        self.prev_error = error;
        if self.abort_on_negative && improvement < T::zero() {
            // Negative improvement, and instant abort is requested
            return false;
        }
        if improvement > self.threshold {
            // positive improvement: reset no-improv-counter
            self.no_improvement_counter = 0;
        } else {
            // Still no improvement, count 1 up
            self.no_improvement_counter += 1;
        }
        self.no_improvement_counter < self.x
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_no_improvement_f32() { test_no_improvement::<f32>(); }
    #[test]
    fn test_no_improvement_f64() { test_no_improvement::<f64>(); }

    fn test_no_improvement<T: Primitive>() {
        {
            let mut abort_strategy = AbortStrategy::NoImprovement {
                threshold: T::from(0.0005).unwrap(),
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), false);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovement {
                threshold: T::from(0.0005).unwrap(),
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2999.99959).unwrap()), false);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovement {
                threshold: T::from(0.0005).unwrap(),
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2999.99935).unwrap()), true);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovement {
                threshold: T::from(0.0005).unwrap(),
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.99).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.99999999).unwrap()), false);
        }
    }

    #[test]
    fn test_no_improvement_for_x_iterations_f32() { test_no_improvement_for_x_iterations::<f32>(); }

    #[test]
    fn test_no_improvement_for_x_iterations_f64() { test_no_improvement_for_x_iterations::<f64>(); }

    fn test_no_improvement_for_x_iterations<T: Primitive>() {
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 1,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: false,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), false);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 1,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: false,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2999.99959).unwrap()), false);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 1,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: false,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2999.99935).unwrap()), true);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 1,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: false,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.99).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.99999999).unwrap()), false);
        }
        // ABORT_ON_NEGATIVE (without negative improvements)
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 1,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), false);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 1,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2999.99959).unwrap()), false);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 1,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2999.99935).unwrap()), true);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 1,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.99).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.99999999).unwrap()), false);
        }
        // ABORT_ON_NEGATIVE (with negative improvements)
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 2,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(3001.0).unwrap()), false);
        }
        {
            // Should abort on negative improvement, even ifs absolute value < threshold
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 2,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(3000.0004).unwrap()), false);
        }
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 2,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(3000.0007).unwrap()), false);
        }

        // X != 1
        {
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 2,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: false,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.0).unwrap()), false);
        }
        {
            // Same as directly above, but with abort_on_negative = true
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 2,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.0).unwrap()), false);
        }
        {
            // Negative improvement before no_improvement_counter == 2
            let mut abort_strategy = AbortStrategy::NoImprovementForXIterations {
                x: 2,
                threshold: T::from(0.0005).unwrap(),
                abort_on_negative: true,
            }
            .create_logic();
            assert_eq!(abort_strategy.next(T::from(3000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2000.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(1999.0).unwrap()), true);
            assert_eq!(abort_strategy.next(T::from(2999.0).unwrap()), false);
        }
    }
}