在减少值上保留先前的值
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我正在尝试创建汽车的模型年份数组，因此模型年份是此处的唯一键，如果存在，则应仅将其添加到totalMilage中。
我知道如何使用年作为年份数组的标识符，但是在这种特定情况下，我只需要一个常规标识符[0, 1, 2]。
这是我想做的事情和我开始做的事情
const data = [
year: 2001,
car: 'Audi',
nrOfDoors: 5
,
year: 2010,
car: 'Audi',
nrOfDoors: 3,
milage: 2000
,
year: 2019,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2005,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2009,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2002,
car: 'Audi',
nrOfDoors: 4,
milage: 2000
,
year: 2001,
car: 'Audi',
nrOfDoors: 3,
milage: 2000
,
year: 2001,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
]
const newList = data.reduce((acc, cur, idx) =>
// try to keep track of previous year, previourYear below
// create one array for unique years and add the milage to total
// create array with this structure
// if (previousYear !== cur.year)
// acc =
// year: cur.year,
// totalMilage: 0
//
//
return acc
, [])这是“命名”数组的处理方法
const data = [
year: 2001,
car: 'Audi',
nrOfDoors: 5
,
year: 2010,
car: 'Audi',
nrOfDoors: 3,
milage: 2000
,
year: 2019,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2005,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2009,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2002,
car: 'Audi',
nrOfDoors: 4,
milage: 2000
,
year: 2001,
car: 'Audi',
nrOfDoors: 3,
milage: 2000
,
year: 2001,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
]
let newList = data.reduce((accumulator, currentValue) =>
const key = currentValue.year
if (accumulator[key] === undefined)
accumulator[key] =
year: key,
totalMilage: 0
accumulator[key].totalMilage += accumulator[key].totalMilage + currentValue.milage
return accumulator
, [])答案
我建议使用对象来更轻松地跟踪您到目前为止所看的年份。然后，如果需要，可以使用Object.entries将对象还原为数组。
const data = [
year: 2001,
car: 'Audi',
nrOfDoors: 5
,
year: 2010,
car: 'Audi',
nrOfDoors: 3,
milage: 2000
,
year: 2019,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2005,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2009,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
,
year: 2002,
car: 'Audi',
nrOfDoors: 4,
milage: 2000
,
year: 2001,
car: 'Audi',
nrOfDoors: 3,
milage: 2000
,
year: 2001,
car: 'Audi',
nrOfDoors: 5,
milage: 2000
];
const summed = data.reduce((acc, el) =>
if(!acc[el.year])
acc[el.year] = 0;
acc[el.year] += el.milage;
return acc;
, )
console.log(summed);
const summedArr = Object.entries(summed).reduce((acc, item) =>
acc.push( year: item[0], milage: item[1] );
return acc;
, [])
console.log(summedArr);另一答案
[如果您只是想按年份获取总里程数，则可以这样做：
const data = [
year: 2001,
car: 'Audi',
nrOfDoors: 5,
,
year: 2010,
car: 'Audi',
nrOfDoors: 3,
milage: 2000,
,
year: 2019,
car: 'Audi',
nrOfDoors: 5,
milage: 2000,
,
year: 2005,
car: 'Audi',
nrOfDoors: 5,
milage: 2000,
,
year: 2009,
car: 'Audi',
nrOfDoors: 5,
milage: 2000,
,
year: 2002,
car: 'Audi',
nrOfDoors: 4,
milage: 2000,
,
year: 2001,
car: 'Audi',
nrOfDoors: 3,
milage: 2000,
,
year: 2001,
car: 'Audi',
nrOfDoors: 5,
milage: 2000,
,
];
const newList = data.reduce((acc, d) =>
if(!acc[d.year])
acc[d.year] = 0;
acc[d.year] += d.milage ? d.milage : 0;
return acc;
, );
[基本上，如果累加器对象还没有该年份，则只需创建它并将其设置为零。然后，按年份将当前对象的里程添加到我们的累加器中。
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