touchstone_rs/metrics/
thresholding.rs

1/// Strategy for computing a decision threshold from anomaly scores.
2pub trait Threshold: Send + Sync {
3    /// Computes the threshold value from the given scores.
4    fn threshold(&self, scores: &[f32]) -> f32;
5    /// Returns the name of this threshold strategy.
6    #[allow(dead_code)]
7    fn name(&self) -> &str;
8}
9
10/// Fixed score threshold.
11#[allow(dead_code)]
12pub struct FixedValueThreshold(pub f32);
13
14/// Threshold at the p-th percentile of scores (p in 0–100).
15pub struct PercentileThreshold(pub f64);
16
17/// Threshold at mean + k * std.
18#[allow(dead_code)]
19pub struct SigmaThreshold(pub f64);
20
21impl Threshold for FixedValueThreshold {
22    fn threshold(&self, _scores: &[f32]) -> f32 {
23        self.0
24    }
25    fn name(&self) -> &str {
26        "fixed"
27    }
28}
29
30impl Threshold for PercentileThreshold {
31    fn threshold(&self, scores: &[f32]) -> f32 {
32        let mut sorted = scores.to_vec();
33        sorted.sort_by(|a, b| a.total_cmp(b));
34        let idx = ((self.0 / 100.0) * (sorted.len() - 1) as f64).round() as usize;
35        sorted[idx.min(sorted.len() - 1)]
36    }
37    fn name(&self) -> &str {
38        "percentile"
39    }
40}
41
42impl Threshold for SigmaThreshold {
43    fn threshold(&self, scores: &[f32]) -> f32 {
44        let n = scores.len() as f64;
45        let mean = scores.iter().map(|&s| s as f64).sum::<f64>() / n;
46        let var = scores
47            .iter()
48            .map(|&s| (s as f64 - mean).powi(2))
49            .sum::<f64>()
50            / n;
51        (mean + self.0 * var.sqrt()) as f32
52    }
53    fn name(&self) -> &str {
54        "sigma"
55    }
56}
57
58/// Binarizes scores using a threshold: 1 if score >= threshold, 0 otherwise.
59pub(crate) fn apply_threshold(scores: &[f32], thresh: f32) -> Vec<u8> {
60    scores
61        .iter()
62        .map(|&s| if s >= thresh { 1 } else { 0 })
63        .collect()
64}
touchstone_rs/metrics/thresholding.rs

touchstone_rs/metrics/
thresholding.rs
