Javascript - 如何计算数组 reduce() 方法中对象数组的唯一 ID(值)

Question

您好，我一直在练习 reduce 方法的挑战以真正理解它，但这个主题让我感到困惑。

const orders = [
    {  livingId: 996, cash: 30500.35, tax: 0.06, isDisputed: true},
    {  livingId: 910, cash: 100, tax: 0.08, isDisputed: true },
    {  livingId: 912, cash: 4200.11, tax: 0.06 },
    {  livingId: 996, cash: 99.12, tax: 0.06, isDisputed: false },
    {  livingId: 910, cash: 0.00, tax: 0.08, isShipped: true },
    {  livingId: 996, cash: 10, tax: 0.06, isDisputed: true },
];

const result = orders.reduce(
    (arr, current) => {
        const numOrders = arr.numOrders + 1;
        const uniqueId = [...new Set([current.livingId])] //returns [996]
        console.log("arr.uniqueId= "+ arr.uniqueId)
        console.log("current.livingId= "+ current.livingId)  
        console.log("current.livingId  + arr.uniqueId= "+ uniqueId)
 return {
            numOrders,
            uniqueId,
        };
    },
    {
        numOrders: 0, 
        uniqueId: 0,
    },
);

console.log(result)

如何从 livingId 返回唯一 ID 值的总数？连同我当前获取总订单的方法。

预期结果:订单数:6livingId: 3

我已经尝试在控制台记录多种方法，如 filter、includes 并发现最干净的是新的 Set 方法，但它只返回来自返回 [996] 的 livingId 的最后一个可迭代数组。返回的 .length 肯定是 1 而不是 3。我也试过这个，但它返回所有值。

const uniqueId = [...new Set([arr.uniqueId, current.livingId])] // 0,996,910,912,996,910,996

Answer 1

如果你想用reduce来做到这一点:

const orders=[{livingId:996,cash:30500.35,tax:.06,isDisputed:!0},{livingId:910,cash:100,tax:.08,isDisputed:!0},{livingId:912,cash:4200.11,tax:.06},{livingId:996,cash:99.12,tax:.06,isDisputed:!1},{livingId:910,cash:0,tax:.08,isShipped:!0},{livingId:996,cash:10,tax:.06,isDisputed:!0}];

const ids = orders.reduce((set, c) => {
  set.add(c.livingId);
  return set;
}, new Set());

console.log(ids.size);

或者:map在数组上获取一个 id 数组，将该数组添加到一个集合中，并获取它的 size .

const orders = [
  {  livingId: 996, cash: 30500.35, tax: 0.06, isDisputed: true},
  {  livingId: 910, cash: 100, tax: 0.08, isDisputed: true },
  {  livingId: 912, cash: 4200.11, tax: 0.06 },
  {  livingId: 996, cash: 99.12, tax: 0.06, isDisputed: false },
  {  livingId: 910, cash: 0.00, tax: 0.08, isShipped: true },
  {  livingId: 996, cash: 10, tax: 0.06, isDisputed: true }
];

const idsLen = new Set(orders.map(order => order.livingId)).size;

console.log(idsLen);