feat: add groupBy

src/groupBy.ts

@@ -0,0 +1,26 @@
+import get from './get'
+import { ToPathValue } from './toPath'
+
+/**
+ * 根据 `iteratee` 对 `arr` 进行分组。
+ *
+ * @param arr 要分组的数据
+ * @param iteratee 迭代值，字符串或数字表示键路径，函数表示以该函数生成 `key`
+ * @returns 分组结果
+ */
+export default function groupBy<T>(
+  arr: T[],
+  iteratee: ToPathValue | ((item: T, index: number) => any)
+): { [key: string]: T[] } {
+  const iterateeIsFunction = typeof iteratee === 'function'
+  return arr.reduce<{ [key: string]: T[] }>((res, item, index) => {
+    const key = iterateeIsFunction
+      ? (iteratee as any)(item, index)
+      : get(item as any, iteratee as any)
+    if (!res[key]) {
+      res[key] = []
+    }
+    res[key].push(item)
+    return res
+  }, {})
+}

src/index.ts

@@ -21,6 +21,7 @@ export { default as formatDate } from './formatDate'
 export { default as formatDateDiff } from './formatDateDiff'
 export { default as get } from './get'
 export { default as getType } from './getType'
+export { default as groupBy } from './groupBy'
 export { default as has } from './has'
 export { default as inBrowser } from './inBrowser'
 export { default as inNode } from './inNode'

src/keyBy.ts

@@ -13,12 +13,12 @@ export default function keyBy<T>(
   iteratee: ToPathValue | ((item: T, index: number) => any)
 ): { [key: string]: T } {
   const iterateeIsFunction = typeof iteratee === 'function'
-  return arr.reduce((res, item, index) => {
+  return arr.reduce<{ [key: string]: T }>((res, item, index) => {
     res[
       iterateeIsFunction
         ? (iteratee as any)(item, index)
         : get(item as any, iteratee as any)
     ] = item
     return res
-  }, {} as any)
+  }, {})
 }

test/index.test.ts

@@ -1591,3 +1591,11 @@ describe('chunk', () => {
     expect(vtils.chunk([1, 2, 3], 2, 4)).toEqual([[1, 2], [3, 4]])
   })
 })
+
+describe('groupBy', () => {
+  test('ok', () => {
+    expect(vtils.groupBy([6.1, 4.2, 6.3], Math.floor)).toEqual({ 4: [4.2], 6: [6.1, 6.3] })
+    expect(vtils.groupBy(['one', 'two', 'three'], 'length')).toEqual({ 3: ['one', 'two'], 5: ['three'] })
+    expect(vtils.groupBy([{ i: 1 }, { i: 2 }, { i: 2, x: 0 }], 'i')).toEqual({ 1: [{ i: 1 }], 2: [{ i: 2 }, { i: 2, x: 0 }] })
+  })
+})