fix: median aggregation function (#4837)

Author: tombuntus

packages/table-core/src/aggregationFns.ts

@@ -1,4 +1,5 @@
 import { AggregationFn } from './features/Grouping'
+import { isNumberArray } from './utils'
 
 const sum: AggregationFn<any> = (columnId, _leafRows, childRows) => {
   // It's faster to just add the aggregations together instead of
@@ -82,18 +83,17 @@ const median: AggregationFn<any> = (columnId, leafRows) => {
     return
   }
 
-  let min = 0
-  let max = 0
-
-  leafRows.forEach(row => {
-    let value = row.getValue(columnId)
-    if (typeof value === 'number') {
-      min = Math.min(min, value)
-      max = Math.max(max, value)
-    }
-  })
+  const values = leafRows.map(row => row.getValue(columnId))
+  if (!isNumberArray(values)) {
+    return
+  }
+  if (values.length === 1) {
+    return values[0]
+  }
 
-  return (min + max) / 2
+  const mid = Math.floor(values.length / 2)
+  const nums = values.sort((a, b) => a - b)
+  return values.length % 2 !== 0 ? nums[mid] : (nums[mid - 1]! + nums[mid]!) / 2
 }
 
 const unique: AggregationFn<any> = (columnId, leafRows) => {

packages/table-core/src/utils.ts

@@ -103,6 +103,10 @@ export function isFunction<T extends AnyFunction>(d: any): d is T {
   return d instanceof Function
 }
 
+export function isNumberArray(d: any): d is number[] {
+  return Array.isArray(d) && d.every(val => typeof val === 'number')
+}
+
 export function flattenBy<TNode>(
   arr: TNode[],
   getChildren: (item: TNode) => TNode[]