JavaScript：将二维数组与 Map 转换为字典（嵌套对象）

Question

我在一个二维数组中有一组值。我映射了一个对象并创建了一个新数组。 第一个值key 是一个字符串，第二个值currentTasks[key] 是一个数组，其中每个值都有id、text 和date。

const newArray = Object.keys(currentTasks).map(function(key){
                return [key, currentTasks[key]];
            });

newArray 有这样的形式……

['1', {id:'1', text: "Todo item #1", date: '2021-11-30'}]

我要做的是将newArray转换成字典的形式。我想以 HashMap 形式将第一个值作为键，将第二个值作为值。如何将这种形式的数组转换为键值对之类的哈希映射？

{
        '1': {id:'1', text: "Todo item #1", date: '2021-11-30'},
        '2': {id:'2', text: "Todo item #2", date: '2021-12-12'},
        '3': {id:'3', text: "Todo item #3", date: '2021-11-29'},
        '4': {id:'4', text: "Todo item #4", date: '2021-12-03'},
}

我想得到一个这样的嵌套对象数组。

Answer 1

const testValues = [
        ['1', {id:'1', text: "Todo item #1", date: '2021-11-30'}],
        ['2', {id:'2', text: "Todo item #2", date: '2021-12-12'}],
        ['3', {id:'3', text: "Todo item #3", date: '2021-11-29'}],
        ['4', {id:'4', text: "Todo item #4", date: '2021-12-03'}]
];

const outputObject = {};
testValues.forEach(x => {
  outputObject[x[0]] = x[1];
});

console.log(testValues, outputObject);

Answer 2

如果您为了简洁，我相信您正在寻找reduce 数组方法。

reduce() 方法按顺序对数组的每个元素执行用户提供的“reducer”回调函数，传入前一个元素的计算返回值。在数组的所有元素上运行 reducer 的最终结果是单个值。

您可以提供一个初始值，在这种情况下，它是一个对象字面量。然后，您可以映射每个子数组并提供键：值对。

const array1 = [
        ['1', {id:'1', text: "Todo item #1", date: '2021-11-30'}],
        ['2', {id:'2', text: "Todo item #2", date: '2021-12-12'}],
        ['3', {id:'3', text: "Todo item #3", date: '2021-11-29'}],
        ['4', {id:'4', text: "Todo item #4", date: '2021-12-03'}]
];
const reducer = (previousValue, currentValue) => ({...previousValue, [currentValue[0]]: currentValue[1]});

// {1: {…}, 2: {…}, 3: {…}, 4: {…}}
console.log(array1.reduce(reducer, {}));

// as a one liner 
// array1.reduce((a, b) => ({...a, [b[0]]: b[1]}), {})

或者 你也可以使用Map

Map 对象保存键值对并记住键的原始插入顺序。任何值（对象和原始值）都可以用作键或值。

const array1 = [
        ['1', {id:'1', text: "Todo item #1", date: '2021-11-30'}],
        ['2', {id:'2', text: "Todo item #2", date: '2021-12-12'}],
        ['3', {id:'3', text: "Todo item #3", date: '2021-11-29'}],
        ['4', {id:'4', text: "Todo item #4", date: '2021-12-03'}]
];
const newMap = new Map()

array1.forEach(el => newMap.set(el[1], el[0]))



// 1: {…}, 2: {…}, 3: {…}, 4: {…}
newMap.forEach((key, value) => console.log(key, value))

Answer 3

我猜这就是你要找的输出？：

const values = [
        ['1', {id:'1', text: "Todo item #1", date: '2021-11-30'}],
        ['2', {id:'2', text: "Todo item #2", date: '2021-12-12'}],
        ['3', {id:'3', text: "Todo item #3", date: '2021-11-29'}],
        ['4', {id:'4', text: "Todo item #4", date: '2021-12-03'}]
]

const obj = {};

values.map(val => obj[val[0]] = val[1])

console.log(obj)

Answer 4

使用Object.fromEntries -

const input = [
  {id:'1', text: "Todo item #1", date: '2021-11-30'},
  {id:'2', text: "Todo item #2", date: '2021-12-12'},
  {id:'3', text: "Todo item #3", date: '2021-11-29'},
  {id:'4', text: "Todo item #4", date: '2021-12-03'},
]

const output =
  Object.fromEntries(input.map(x => [x.id, x]))
  
console.log(output)

{
  '1': {id:'1', text: "Todo item #1", date: '2021-11-30'},
  '2': {id:'2', text: "Todo item #2", date: '2021-12-12'},
  '3': {id:'3', text: "Todo item #3", date: '2021-11-29'},
  '4': {id:'4', text: "Todo item #4", date: '2021-12-03'},
}