fix(table-core): prevent median aggregation overflow for large finite values

.changeset/fix-median-overflow.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/table-core': patch
+---
+
+Fix even-length median aggregation overflowing to `Infinity` when middle values are large and finite

packages/table-core/src/features/row-aggregation/aggregationFns.ts

@@ -294,9 +294,15 @@ export const aggregationFn_median = /* @__PURE__ */ constructAggregationFn<
     if (!values.length) return undefined
     values.sort((a, b) => a - b)
     const mid = Math.floor(values.length / 2)
-    return values.length % 2
-      ? values[mid]
-      : (values[mid - 1]! + values[mid]!) / 2
+    if (values.length % 2) {
+      return values[mid]
+    }
+    const a = values[mid - 1]!
+    const b = values[mid]!
+    const sum = a + b
+    return Number.isFinite(sum) || !Number.isFinite(a) || !Number.isFinite(b)
+      ? sum / 2
+      : a / 2 + b / 2
   },
 })
 

packages/table-core/tests/unit/fns/aggregationFns.test.ts

@@ -99,6 +99,43 @@ describe('aggregation function definitions', () => {
     ).toBeUndefined()
   })
 
+  it('does not overflow median for large finite values and preserves subnormals', () => {
+    // Large finite values whose intermediate sum overflows to Infinity
+    expect(
+      aggregationFn_median.aggregate(
+        context([Number.MAX_VALUE, Number.MAX_VALUE]),
+      ),
+    ).toBe(Number.MAX_VALUE)
+    expect(
+      aggregationFn_median.aggregate(
+        context([-Number.MAX_VALUE, -Number.MAX_VALUE]),
+      ),
+    ).toBe(-Number.MAX_VALUE)
+    expect(
+      aggregationFn_median.aggregate(context([1e308, 1.5e308])),
+    ).toBe(1.25e308)
+
+    // Subnormal / tiny values are preserved without underflow to 0
+    expect(
+      aggregationFn_median.aggregate(
+        context([Number.MIN_VALUE, Number.MIN_VALUE]),
+      ),
+    ).toBe(Number.MIN_VALUE)
+
+    // Infinity, NaN, and control checks
+    expect(
+      aggregationFn_median.aggregate(context([Infinity, Infinity])),
+    ).toBe(Infinity)
+    expect(
+      aggregationFn_median.aggregate(context([-Infinity, -Infinity])),
+    ).toBe(-Infinity)
+    expect(
+      Number.isNaN(
+        aggregationFn_median.aggregate(context([-Infinity, Infinity]))!,
+      ),
+    ).toBe(true)
+  })
+
   it('uses Set semantics for unique values', () => {
     expect(
       aggregationFn_unique.aggregate(context(['a', null, undefined, 'a'])),