flow like the river

BACK_BACK/node_modules/index-array-by/README.md

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+index-array-by
+==============
+
+[![NPM package][npm-img]][npm-url]
+[![Build Size][build-size-img]][build-size-url]
+[![NPM Downloads][npm-downloads-img]][npm-downloads-url]
+
+A utility function to index arrays by any criteria.
+
+`indexBy(list, keyAccessors, multiItem = true)`
+
+## Quick start
+
+```js
+import indexBy from 'index-array-by';
+```
+or using a *script* tag
+```html
+<script src="//unpkg.com/index-array-by"></script>
+```
+
+## Usage example
+
+Given an array
+```js
+const people = [
+    { name: 'Mary', surname: 'Jane', age: 28 },
+    { name: 'John', surname: 'Smith', age: 24 },
+    { name: 'John', surname: 'Doe', age: 32 }
+];
+```
+
+Use `indexBy` to index it by a given attribute (string type `keyAccessor`) or any other custom criteria (function type `keyAccessor`). You can also pass an array of `keyAccessors` to retrieve a nested object recursively indexed by the multiple keys.
+
+Use the third parameter (`multiItem`) to indicate whether each key should point to a single item (unadvised if the keys are not unique) or an array of multiple items (default behavior). 
+
+```js
+indexBy(people, 'surname', false);
+
+// Result: 
+{
+ Doe: { name: 'John', age: 32 },
+ Jane: { name: 'Mary', age: 28 },
+ Smith: { name: 'John', age: 24 }
+}
+```
+
+```js
+indexBy(people, 'name', true);
+
+// Result: 
+{
+  Mary: [ { surname: 'Jane', age: 28 } ],
+  John: [
+    { surname: 'Smith', age: 24 },
+    { surname: 'Doe', age: 32 }
+  ]
+}
+```
+
+```js
+indexBy(people, ({ name, surname }) => `${surname}, ${name}`, false);
+
+// Result: 
+{
+ 'Jane, Mary': { name: 'Mary', surname: 'Jane', age: 28 },
+ 'Smith, John': { name: 'John', surname: 'Smith', age: 24 },
+ 'Doe, John': { name: 'John', surname: 'Doe', age: 32 }
+}
+```
+
+```js
+indexBy(people, ['name', 'surname'], false));
+
+// Result: 
+{
+ Mary: { Jane: { age: 28 }},
+ John: { Smith: { age: 24 }, Doe: { age: 32 }}
+}
+```
+
+```js
+indexBy(people, ({ age }) => `${Math.floor(age / 10) * 10}s`, true);
+
+// Result: 
+{
+  '20s': [
+    { name: 'Mary', surname: 'Jane', age: 28 },
+    { name: 'John', surname: 'Smith', age: 24 },
+  ],
+  '30s': [{ name: 'John', surname: 'Doe', age: 32 }]
+}
+```
+
+
+The `multiItem` parameter also accepts a transformation function with the method to reduce multiple items into a single one. In this case, it's keeping only the max age.
+
+```js
+indexBy(people, 'name', items => Math.max(...items.map(item => item.age)));
+
+// Result:
+
+{
+  John: 32,
+  Mary: 28
+}
+```
+
+
+A fourth optional parameter (`flattenKeys`) (default: `false`) allows you to receive a flat array structure instead of the default nested format, with each item formatted as `{ keys: [<ordered unique keys for the item>], vals: <single or multiple item> }`.
+
+```js
+indexBy(people, ['name', 'surname'], true, true));
+
+// Result: 
+[
+  { keys: ['Mary', 'Jane'], vals: [{ age: 28 }] },
+  { keys: ['John', 'Smith'], vals: [{ age: 24 }] },
+  { keys: ['John', 'Doe'], vals: [{ age: 32 }] }
+]
+```
+
+
+[npm-img]: https://img.shields.io/npm/v/index-array-by
+[npm-url]: https://npmjs.org/package/index-array-by
+[build-size-img]: https://img.shields.io/bundlephobia/minzip/index-array-by
+[build-size-url]: https://bundlephobia.com/result?p=index-array-by
+[npm-downloads-img]: https://img.shields.io/npm/dt/index-array-by
+[npm-downloads-url]: https://www.npmtrends.com/index-array-by