Expose the number of observations

composer.json

@@ -11,7 +11,7 @@
     ],
     "require": {
         "php": "^8.1",
-        "sanmai/pipeline": "^6.8",
+        "sanmai/pipeline": "^6.11",
         "tumblr/chorus-timekeeper": "^0.1.0"
     },
     "require-dev": {

src/AnomalyDetectionResult.php

@@ -48,6 +48,9 @@
      */
     public const DIRECTION_DOWN = 'down';
 
+    /** @var int The number of observations */
+    private int $count;
+
     /** @var float The standard deviation */
     private float $std_dev;
 
@@ -75,32 +78,34 @@
     /**
      * Create a new anomaly detection result instance.
      *
+     * @param int $count The number of observations
      * @param float $std_dev The standard deviation
      * @param float $mean The mean value
      * @param float $latest The latest value
      * @param float|int $sensitivity The sensitivity (see `SlidingWindowCounter::detectAnomaly()`)
      */
-    public function __construct(float $std_dev, float $mean, float $latest, float|int $sensitivity)
+    public function __construct(int $count, float $std_dev, float $mean, float $latest, float|int $sensitivity)
     {
+        $this->count = $count;
         $this->std_dev = $std_dev;
         $this->mean = $mean;
         $this->latest = $latest;
         $this->sensitivity = $sensitivity;
 
         $this->high = ceil($this->mean + ($sensitivity * $this->std_dev));
         $this->low = floor($this->mean - ($sensitivity * $this->std_dev));
 
         if ($this->latest >= $this->low && $this->latest <= $this->high) {
             return;
         }
 
         if ($this->std_dev > 0.0) {
             $this->hops = abs($this->mean - $this->latest) / $this->std_dev;
         }
 
         if ($this->latest < $this->low) {
             $this->direction = self::DIRECTION_DOWN;
         } elseif ($this->latest > $this->high) {
             $this->direction = self::DIRECTION_UP;
         }
     }
@@ -118,7 +123,7 @@
      *
      * @param int $precision the number of decimal digits to round to
      */
     public function toArray(int $precision = 2): array
     {
         return array_map(
             fn ($val) => is_float($val) ? round($val, $precision) : $val,
@@ -126,6 +131,14 @@
         );
     }
 
+    /**
+     * The number of observations
+     */
+    public function getCount(): int
+    {
+        return $this->count;
+    }
+
     /**
      * The standard deviation.
      */

src/SlidingWindowCounter.php

@@ -249,6 +249,7 @@ public function detectAnomaly(string $bucket_key, float|int $sensitivity = 2, ?i
         $variance = $this->getHistoricVariance($bucket_key, $start_time);
 
         return new AnomalyDetectionResult(
+            $variance->getCount(),
             $variance->getStandardDeviation(),
             $variance->getMean(),
             $this->getLatestValue($bucket_key),

tests/AnomalyDetectionResultTest.php

@@ -35,12 +35,13 @@ final class AnomalyDetectionResultTest extends TestCase
      */
     public function testHappyPath(): void
     {
-        $result = new AnomalyDetectionResult(0.999, 10.0, 11.0, 1);
+        $result = new AnomalyDetectionResult(10, 0.999, 10.0, 11.0, 1);
 
         $this->assertFalse($result->isAnomaly());
         $this->assertSame(AnomalyDetectionResult::DIRECTION_NONE, $result->getDirection());
 
         $this->assertSame([
+            'count' => 10,
             'std_dev' => 1.0,
             'mean' => 10.0,
             'sensitivity' => 1,
@@ -57,8 +58,9 @@ public function testHappyPath(): void
      */
     public function testAllGetters(): void
     {
-        $result = new AnomalyDetectionResult(1.0, 10.0, 11.0, 0.9);
+        $result = new AnomalyDetectionResult(11, 1.0, 10.0, 11.0, 0.9);
 
+        $this->assertSame(11, $result->getCount());
         $this->assertSame(1.0, $result->getStandardDeviation());
         $this->assertSame(10.0, $result->getMean());
         $this->assertSame(0.9, $result->getSensitivity());
@@ -74,11 +76,12 @@ public function testAllGetters(): void
      */
     public function testAnomalyDirectionUp(): void
     {
-        $result = new AnomalyDetectionResult(1.0, 10.0, 12.011, 1);
+        $result = new AnomalyDetectionResult(22, 1.0, 10.0, 12.011, 1);
 
         $this->assertTrue($result->isAnomaly());
 
         $this->assertSame([
+            'count' => 22,
             'std_dev' => 1.0,
             'mean' => 10.0,
             'sensitivity' => 1,
@@ -95,11 +98,12 @@ public function testAnomalyDirectionUp(): void
      */
     public function testAnomalyDetectionDown(): void
     {
-        $result = new AnomalyDetectionResult(1.0, 10.0, 1.123456, 3);
+        $result = new AnomalyDetectionResult(33, 1.0, 10.0, 1.123456, 3);
 
         $this->assertTrue($result->isAnomaly());
 
         $this->assertSame([
+            'count' => 33,
             'std_dev' => 1.0,
             'mean' => 10.0,
             'sensitivity' => 3,
@@ -142,7 +146,7 @@ public static function providerDirections(): iterable
      */
     public function testDirections(float $latest, bool $expected_is_anomaly, string $expected_direction): void
     {
-        $result = new AnomalyDetectionResult(1.0, 10.0, $latest, 1);
+        $result = new AnomalyDetectionResult(100, 1.0, 10.0, $latest, 1);
 
         $this->assertSame($expected_is_anomaly, $result->isAnomaly(), 'Unexpected anomaly result');
         $this->assertSame($expected_direction, $result->getDirection(), 'Unexpected direction');

tests/SlidingWindowCounterTest.php

@@ -113,7 +113,7 @@ public function testIncrementThrowsTimeInPast(): void
         $window_size = 60;
         $observation_period = 1000;
 
-        $counter = new SlidingWindowCounter('default', 60, $observation_period, new FakeCache(), $time_keeper);
+        $counter = new SlidingWindowCounter('default', $window_size, $observation_period, new FakeCache(), $time_keeper);
 
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessageMatches('/The time provided \(\d+\) is too far in the past \(current time: \d+, observation period: 1000\)/');
@@ -248,6 +248,7 @@ public function testVariance(): void
         $this->assertSame(5, $counter->getHistoricVariance('test')->getCount());
 
         $this->assertSame([
+            'count' => 5,
             'std_dev' => 7.24,
             'mean' => 6.82,
             'sensitivity' => 3,