fix: median absolute deviation calculation (#236)

Signed-off-by: Péter Pallos <pallosp@gmail.com>
Signed-off-by: Jérôme Benoit <jerome.benoit@piment-noir.org>

Author: jerome-benoit

src/utils.ts

@@ -265,6 +265,15 @@ const quantileSorted = (samples: number[], q: number) => {
   return samples[baseIndex]
 }
 
+/**
+ * Computes the median of a sample.
+ * @param samples - the sample
+ * @returns the median of the sample
+ */
+const median = (samples: number[]) => {
+  return medianSorted(samples.sort((a, b) => a - b))
+}
+
 /**
  * Computes the median of a sorted sample.
  * @param samples - the sorted sample
@@ -316,7 +325,7 @@ export const getStatisticsSorted = (samples: number[]): Statistics => {
     aad: absoluteDeviation(samples, average, mean),
     critical,
     df,
-    mad: absoluteDeviation(samples, medianSorted, p50),
+    mad: absoluteDeviation(samples, median, p50),
     // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
     max: samples[df]!,
     mean,

test/utils.test.ts

@@ -0,0 +1,8 @@
+import { expect, test } from 'vitest'
+
+import { getStatisticsSorted } from '../src/utils'
+
+test('median absolute deviation', () => {
+  const stats = getStatisticsSorted([1, 2, 3])
+  expect(stats.mad).toBe(1)
+})