Code snippet from The Coding Café - snippet-8.java

snippet-8.java

public static Gatherer<Double, ?, Double> movingAverage(int windowSize) {
    return Gatherer.of(
        LinkedList::new,  // 1️⃣ Use LinkedList for efficient add/remove
        (window, price, downstream) -> {
            window.add(price);                    // 2️⃣ Add new price to window
            if (window.size() > windowSize) {     // 3️⃣ Window too big?
                window.removeFirst();             // 4️⃣ Remove oldest price
            }
            if (window.size() == windowSize) {    // 5️⃣ Window full?
                double avg = window.stream()
                    .mapToDouble(Double::doubleValue)
                    .average()
                    .orElse(0.0);
                return downstream.push(avg);      // 6️⃣ Emit moving average
            }
            return true;  // 7️⃣ Keep gathering (building up window)
        }
    );
}

// Usage example:
// Prices: [100, 102, 101, 105, 103, 107, 104]
// Window size 3:
//   [100, 102, 101] → avg: 101.0
//   [102, 101, 105] → avg: 102.7
//   [101, 105, 103] → avg: 103.0
//   ... sliding window continues