如果你想轻松地对数组中的项进行分组(类似于SQL中的GROUP BY),那么欢迎使用新方法array.groupBy() 和 array.groupByToMap()。 两个函数都接受一个回调函数,该回调函数应返回必须插入当前项的组的键。 array.groupBy()将这些项分组为一个普通的JavaScript对象,而array.groupByToMap()将它们分组为一个 Map 实例。
Array合并javascriptjsarraygroup by 新的数组组提案(目前处于第三阶段),它引入了新方法array.groupby() 和array.groupbytomap() 。它们的 polyfills 文件可以在 core-js库中找到。 接着,我们来看下能从中学到些什么。1.array.groupBy()假设我们有一个产品列表,其中每个产品都是一个具有2 ...
value: '🍎', }, { type: 'fruit', value: '🍇', }, { type: 'fruit', value: '🍊', }, { type: 'vegetable', value: '🥦', }, { type: 'vegetable', value: '🥕', }, { type: 'vegetable', value: '🌶️', }, ]; 对items数组基于type进行分组,得到的结果如下: { ...
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce groupBy https://learnwithparam.com/blog/how-to-group-by-array-of-objects-using-a-key/ _.groupBy https://lodash.com/docs/4.17.2#groupBy OK
We create an array of objects and group them by their type property. The callback function extracts the type value which becomes the group key. The result is an object with properties matching the group keys. $ node main.js { vegetables: [{ name: 'asparagus', type: 'vegetables' }], ...
代码语言:javascript 代码运行次数:0 运行 AI代码解释 privatevoidwriteMap(final Object value,final MapObjectInspector inspector,final GroupType type){// Get the internal map structure (MAP_KEY_VALUE)GroupType repeatedType=type.getType(0).asGroupType();recordConsumer.startGroup();recordConsumer.startFiel...
json对象,就是一个键对应一个值,使用的是大括号{ },如:{key:value} JSONArray json数组,使用中括号[ ],只不过数组里面的项也是json键值对格式的 Json对象中是添加的键值对,JSONArray中添加的是Json对象 例子 代码语言:javascript 代码运行次数:0 运行 ...
constructorObject.prototype.toString, but the first two may be inaccurate, and the latter is more troublesome. To solve this small problem, JavaScript provides theArray.isArray()method, which returns a boolean value indicating whether the parameter is an array. It can make up for the ...
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap varnew_array = arr.flatMap(functioncallback(currentValue[, index[, array]]) {// return element for new_array}[, thisArg]) flat https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/...
Return Value The accumulated result from the last call of the callback function. Array Tutorials: Array Tutorial Array Const Basic Array Methods Array Search Methods Array Sort Methods Array Iteration Methods Browser Support reduceRight() is an ECMAScript5 (ES5) feature. ES5 (JavaScript 2009) is ...