如何在数组上使用 javascript reduce 方法，该数组是对象属性的值并仅输出正元素的总和？

如何解决如何在数组上使用 javascript reduce 方法，该数组是对象属性的值并仅输出正元素的总和？

我有四个对象（account1、account2、account3、account4）如下，我想获取“所有存款的总和”和“总和”所有提款的”。这里存款和取款显示在移动属性中。这里所有的正值都是存款，负值是取款。但我只想使用没有 flatMap 和 filter 方法的 reduce 方法。我通过执行以下操作获得了所有动作：

---

const transactions = accounts.reduce(
  (acc,cur) => acc.concat(cur.movements),[]
);

这将减少到 [200,450,-400,3000,-650,-130,70,1300,5000,3400,-150,-790,-3210,-1000,8500,-30,200,-200,340,-300,-20,50,400,-460,430,1000,700,90]

但是，如何设置运动数组，以便我可以获得正值（存款）和负值（取款）的总和。

---

const account1 = {
  owner: 'Jonas Schmedtmann',movements: [200,1300],interestRate: 1.2,// %
  pin: 1111,};

const account2 = {
  owner: 'Jessica Davis',movements: [5000,-30],interestRate: 1.5,pin: 2222,};

const account3 = {
  owner: 'Steven Thomas Williams',-460],interestRate: 0.7,pin: 3333,};

const account4 = {
  owner: 'Sarah Smith',movements: [430,90],interestRate: 1,pin: 4444,};

const accounts = [account1,account2,account3,account4];

解决方法

您可以使用过滤器运行两次总和减少，或者同时跟踪正/负总和的组合减少：

const amounts = [200,450,-400,3000,-650,-130,70,1300,5000,3400,-150,-790,-3210,-1000,8500,-30,200,-200,340,-300,-20,50,400,-460,430,1000,700,90];
const pos = amounts.filter(am => am > 0).reduce((tot,v) => tot + v);
const neg = amounts.filter(am => am < 0).reduce((tot,v) => tot + v);
console.log('pos:',pos);
console.log('neg:',neg);

// or alternatively
const combo = amounts.reduce(([pos,neg],val) => val > 0 ? [pos + val,neg] : [pos,neg + val],[0,0]);
console.log('combo:',combo);

,

可能是这个吗？

const
  account1 = { owner: 'Jonas Schmedtmann',movements: [200,1300],interestRate: 1.2,pin: 1111 },account2 = { owner: 'Jessica Davis',movements: [5000,-30],interestRate: 1.5,pin: 2222 },account3 = { owner: 'Steven Thomas Williams',-460],interestRate: 0.7,pin: 3333 },account4 = { owner: 'Sarah Smith',movements: [430,90],interestRate: 1,pin: 4444 }
  ;

const transactions = (...accounts) =>
  accounts.reduce((r,{movements})=>
  { 
  movements.forEach(v =>{ v > 0 ? r.deposits += v : r.withdrawals += v })
  return r
  },{deposits:0,withdrawals:0})

console.log( transactions( account1,account2,account3,account4 ) )  

.as-console-wrapper { max-height: 100% !important; top: 0 }

,

您可以使用 array#reduce 来总结 deposits 和 withdrawals。使用 account 迭代每个 array#reduce，然后使用 movements 迭代每个 array#forEach，在结果累加器中总结 deposits 和 withdrawals。

const result = accounts.reduce((r,{movements}) => {
  movements.forEach(v => {
    v > 0 ? r.deposits += v : r.withdrawals += v;
  });
  return r;
 },{deposits: 0,withdrawals: 0});

const account1 = {
  owner: 'Jonas Schmedtmann',// %
  pin: 1111,};

const account2 = {
  owner: 'Jessica Davis',pin: 2222,};

const account3 = {
  owner: 'Steven Thomas Williams',pin: 3333,};

const account4 = {
  owner: 'Sarah Smith',pin: 4444,};

const accounts = [account1,account4];
const result = accounts.reduce((r,{movements}) => {
  movements.forEach(v => {
    v > 0 ? r.deposits += v : r.withdrawals += v;
  });
  return r;
},withdrawals: 0});
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0 }

,

您可以像这样使用 .reduce 来迭代和累积正负运动。

movements.reduce((acc,movement) => {
  if (movement > 0) acc[0] += movement
  else acc[1] += movement
    
  return acc
},0])

这看起来像一个函数。

let allTransactions = [200,90]

function getPosNeg(movements) {
  return movements.reduce((acc,movement) => {
    if (movement > 0) acc[0] += movement
    else acc[1] += movement
    
    return acc
  },0])
}

let [positive,negative] = getPosNeg(allTransactions)

console.log({positive: positive,negative: negative})