javascript - 删除数组中对象中的重复键并聚合每个状态 Javascript 的总数

Question

我有这个对象数组，我想在 NY 中添加计数但只打印一次 NY 的状态，如何删除重复的键而不是 if 语句中的核心“NY”？

Input

const cityPopulation = [
{ state: 'NJ', city: 'Jersey', count: 100 },
{ state: 'NY', city: 'NYC', count: 100 },
{ state: 'CA', city: 'SFO', count: 100 },
{ state: 'NY', city: 'Albany', count: 100 },]

Output

州计数:新泽西州:100
州计数:纽约州:200
州计数:CA:100

我的方法:

    cityPopulation.forEach(state => {

    if (state.state === 'NY') {
        state.count += state.count
    }

    console.log(`Count for state: ${state.state}: ${state.count}`)

    }
)

Answer 1

你可以用 Array#reduce 来做

const cityPopulation = [ { state: 'NJ', city: 'Jersey', count: 100 }, { state: 'NY', city: 'NYC', count: 100 }, { state: 'CA', city: 'SFO', count: 100 }, { state: 'NY', city: 'Albany', count: 100 },];


let res = Object.values(cityPopulation.reduce((acc, item) => {
  if (acc[item.state]) {
    acc[item.state].count = acc[item.state].count + item.count
  } else {
    acc[item.state] = item
  }
  return acc;
}, {}))

console.log(res)