Updated quantile to use sorted values for min and max

Fixes mathigon#192
sanjayginde · Nov 22, 2024 · ef7f828 · ef7f828
1 parent f7aeeb4
commit ef7f828
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Showing 2 changed files with 10 additions and 2 deletions.
diff --git a/src/statistics.ts b/src/statistics.ts
@@ -19,8 +19,8 @@ export function quantile(values: number[], p: number, method: number = 1): numbe
   if (!n) return 0;
 
   const sorted = values.slice(0).sort((a, b) => (a - b));
-  if (p === 0) return values[0];
-  if (p === 1) return values[n - 1];
+  if (p === 0) return sorted[0];
+  if (p === 1) return sorted[n - 1];
 
   // See https://en.wikipedia.org/wiki/Quantile#Estimating_quantiles_from_a_sample
   if (![1, 2, 3].includes(method)) throw new RangeError('Invalid quantile method.');

diff --git a/test/statistics-test.ts b/test/statistics-test.ts
@@ -35,5 +35,13 @@ tape('quantile', (test) => {
   test.equal(quantile(oddPopulation, 0.5), 3.5);
   test.equal(quantile(oddPopulation, 0.75), 5);
   test.equal(quantile(oddPopulation, 1), 6);
+
+  const randomPopulation = [4, 1, 2, 6, 3, 5];
+  test.equal(quantile(randomPopulation, 0), 1);
+  test.equal(quantile(randomPopulation, 0.25), 2);
+  test.equal(quantile(randomPopulation, 0.5), 3.5);
+  test.equal(quantile(randomPopulation, 0.75), 5);
+  test.equal(quantile(randomPopulation, 1), 6);
+
   test.end();
 });