Struct Anomaly 

pub struct Anomaly<const N: usize> { /* private fields */ }

Flags a reading that lies far from the recent norm.

“Tell me when something is off” needs a baseline: a reading is suspicious only relative to what is usual. An Anomaly keeps a rolling window of recent readings and flags one that sits more than a chosen number of standard deviations from their mean - the three-sigma rule, the standard z-score test, with the threshold left to the caller (3.0 is the usual choice). It is dependency-free: instead of taking a square root it compares the squared deviation against the squared threshold, which is the same test.

With a perfectly flat baseline the spread is zero, so any change at all reads as anomalous; real sensor noise gives a non-zero baseline, where this is not an issue.

A reading that is not a finite number, such as the NaN a failed sensor reports, is always flagged, and is kept out of the baseline so it cannot blind the detector to the readings after it.

Examples

use pamoja_kit::Anomaly;

let mut watch = Anomaly::<8>::new(3.0);
// Establish a steady baseline.
for reading in [10.0, 10.2, 9.8, 10.1, 9.9, 10.0, 10.2, 9.8] {
    watch.check(reading);
}
assert!(!watch.check(10.1)); // close to the norm: fine
assert!(watch.check(20.0)); // a far jump: flagged

Implementations

impl<const N: usize> Anomaly<N>

pub fn new(sigmas: f32) -> Self

Creates a detector that flags readings beyond sigmas standard deviations.

Arguments

• sigmas - the threshold in standard deviations; 3.0 is the common three-sigma rule. Its magnitude is used, and one that is not a number is taken as zero, so the mistake shows as alarms rather than as silence.

Returns

A detector with an empty history.

pub fn with_capacity(sigmas: f32, capacity: usize) -> Self

Creates a detector whose baseline keeps at most capacity readings.

Arguments

• sigmas - the threshold in standard deviations, as for new.
• capacity - the most readings the baseline keeps. One above N is taken as N.

Returns

A detector with an empty history.

pub fn check(&mut self, reading: f32) -> bool

Tests a reading against the recent norm, then folds it into the history.

The reading is judged against the window of earlier readings, so the value being tested does not inflate its own baseline. Until at least two readings have been seen there is no spread to judge against, so nothing is flagged: from the third reading on, a reading can be. A reading that is not a finite number is always flagged and is not kept.

Arguments

• reading - the latest reading.

Returns

true if reading lies more than the configured standard deviations from the mean of the recent window.

pub fn len(&self) -> usize

Returns the number of readings in the baseline window so far.

pub fn is_empty(&self) -> bool

Returns true if no readings have been recorded yet.

pub fn capacity(&self) -> usize

Returns the most readings the baseline keeps: N, or less when made with with_capacity.

Trait Implementations

impl<const N: usize> Clone for Anomaly<N>

fn clone(&self) -> Anomaly<N>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<const N: usize> Copy for Anomaly<N>

impl<const N: usize> Debug for Anomaly<N>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.