Adding sum, min and max to StreamingStat

Author: roberto-butti

CHANGELOG.md

@@ -1,7 +1,7 @@
 # Changelog
 
 ## 1.3.0 - WIP
-- Adding `StreamingStat` class (experimental) for streaming/online computation of mean, variance, stdev, skewness, and kurtosis with O(1) memory
+- Adding `StreamingStat` class (experimental) for streaming/online computation of mean, variance, stdev, skewness, kurtosis, sum, min, and max with O(1) memory
 
 ## 1.2.5 - 2026-02-22
 - Adding `kurtosis()` method for excess kurtosis

README.md

@@ -980,6 +980,9 @@ $s = new StreamingStat();
 $s->add(1)->add(2)->add(3)->add(4)->add(5);
 
 $s->count();     // 5
+$s->sum();       // 15.0
+$s->min();       // 1.0
+$s->max();       // 5.0
 $s->mean();      // 3.0
 $s->variance();  // 2.5
 $s->stdev();     // 1.5811...
@@ -990,6 +993,9 @@ $s->kurtosis();  // -1.2
 | Method | Description | Min n |
 |---|---|---|
 | `count()` | Number of values added | 0 |
+| `sum()` | Sum of all values | 1 |
+| `min()` | Minimum value | 1 |
+| `max()` | Maximum value | 1 |
 | `mean(?int $round = null)` | Arithmetic mean | 1 |
 | `variance(?int $round = null)` | Sample variance | 2 |
 | `pvariance(?int $round = null)` | Population variance | 1 |

src/StreamingStat.php

@@ -24,11 +24,25 @@ class StreamingStat
 
     private float $m4 = 0.0;
 
+    private float $sum = 0.0;
+
+    private float $min = PHP_FLOAT_MAX;
+
+    private float $max = -PHP_FLOAT_MAX;
+
     /**
      * Add a value and update all accumulators using the online algorithm.
      */
     public function add(int|float $value): self
     {
+        $this->sum += $value;
+        if ($value < $this->min) {
+            $this->min = (float) $value;
+        }
+        if ($value > $this->max) {
+            $this->max = (float) $value;
+        }
+
         $n1 = $this->n;
         $this->n++;
         $n = $this->n;
@@ -57,6 +71,42 @@ public function count(): int
         return $this->n;
     }
 
+    /**
+     * Return the sum of all values added.
+     */
+    public function sum(): float
+    {
+        if ($this->n < 1) {
+            throw new InvalidDataInputException("The data must not be empty.");
+        }
+
+        return $this->sum;
+    }
+
+    /**
+     * Return the minimum value added.
+     */
+    public function min(): float
+    {
+        if ($this->n < 1) {
+            throw new InvalidDataInputException("The data must not be empty.");
+        }
+
+        return $this->min;
+    }
+
+    /**
+     * Return the maximum value added.
+     */
+    public function max(): float
+    {
+        if ($this->n < 1) {
+            throw new InvalidDataInputException("The data must not be empty.");
+        }
+
+        return $this->max;
+    }
+
     /**
      * Return the arithmetic mean.
      */

tests/StreamingStatTest.php

@@ -224,4 +224,58 @@ public function test_empty_pvariance_throws(): void
         $this->expectException(InvalidDataInputException::class);
         (new StreamingStat())->pvariance();
     }
+
+    public function test_sum(): void
+    {
+        $data = [1.5, 2.5, 3.0, 4.0, 5.5];
+        $s = $this->fromArray($data);
+        $this->assertEqualsWithDelta(array_sum($data), $s->sum(), self::TOLERANCE);
+    }
+
+    public function test_empty_sum_throws(): void
+    {
+        $this->expectException(InvalidDataInputException::class);
+        (new StreamingStat())->sum();
+    }
+
+    public function test_min(): void
+    {
+        $data = [3, -1, 4, 1, 5, -9, 2, 6];
+        $s = $this->fromArray($data);
+        $this->assertEqualsWithDelta(-9.0, $s->min(), self::TOLERANCE);
+    }
+
+    public function test_empty_min_throws(): void
+    {
+        $this->expectException(InvalidDataInputException::class);
+        (new StreamingStat())->min();
+    }
+
+    public function test_max(): void
+    {
+        $data = [3, -1, 4, 1, 5, -9, 2, 6];
+        $s = $this->fromArray($data);
+        $this->assertEqualsWithDelta(6.0, $s->max(), self::TOLERANCE);
+    }
+
+    public function test_empty_max_throws(): void
+    {
+        $this->expectException(InvalidDataInputException::class);
+        (new StreamingStat())->max();
+    }
+
+    public function test_min_max_single_element(): void
+    {
+        $s = (new StreamingStat())->add(42);
+        $this->assertEqualsWithDelta(42.0, $s->min(), self::TOLERANCE);
+        $this->assertEqualsWithDelta(42.0, $s->max(), self::TOLERANCE);
+    }
+
+    public function test_min_max_negative_values(): void
+    {
+        $data = [-10.5, -3.2, -7.8];
+        $s = $this->fromArray($data);
+        $this->assertEqualsWithDelta(-10.5, $s->min(), self::TOLERANCE);
+        $this->assertEqualsWithDelta(-3.2, $s->max(), self::TOLERANCE);
+    }
 }