add Util.js

2 files changed, 36 insertions, 0 deletions

diff --git a/modules/Util.js b/modules/Util.js
new file mode 100644
index 0000000..cbe466d
--- /dev/null
+++ b/modules/Util.js
@@ -0,0 +1,13 @@
+function useAverage() {
+	var avg = 0;
+	let weight = 0;
+	const append = value => {
+		avg = (weight * avg) + value;
+		weight += 1;
+		avg = avg/weight;
+	}
+
+	return [() => avg, append];
+}
+
+export { useAverage };
diff --git a/modules/Util.test.js b/modules/Util.test.js
new file mode 100644
index 0000000..000d54e
--- /dev/null
+++ b/modules/Util.test.js
@@ -0,0 +1,23 @@
+import { test, assert} from './test-assert.js';
+import { useAverage } from './Util.js';
+
+
+test('Average correctly accumulates an average', () => {
+	let [avg, avg_append] = useAverage();
+	let data = [];
+	for (let i=0; i<5000; i++) {
+		let d = Math.random();
+		data.push(d);
+		avg_append(d);
+	}
+
+	let manual_average = 0;
+	for (let d of data) manual_average += d;
+	manual_average /= data.length;
+
+	const precision = (decimalPlaces, num) => {
+		const theta = 10**decimalPlaces;
+		return Math.floor(num * theta) / theta;
+	};
+	assert.equal(precision(5, avg()), precision(5, manual_average));
+});