javascript - 使用 javascript 根据键对数组中的值进行分组

Question

我有以下数组值，

[
{
    "amount": 4.27,
    "month": 1,
    "year": 2017
},
{
    "amount": 2.46,
    "month": 1,
    "year": 2017
},
{
    "amount": 1.5,
    "month": 2,
    "year": 2017
},
{
    "amount": 28.24,
    "month": 2,
    "year": 2017
},
{
    "amount": 8.24,
    "month": 3,
    "year": 2017
},
{
    "amount": 3.65,
    "month": 3,
    "year": 2017
},
{
    "amount": 0.86,
    "month": 3,
    "year": 2017
},
{
    "amount": 0,
    "month": 1,
    "year": 2018
},
{
    "amount": 71.84,
    "month": 2,
    "year": 2018
},
{
    "amount": 26.62,
    "month": 3,
    "year": 2018
}]

必须根据特定的月和年进行分组，最终值应采用以下格式，

[
{
    "amount": 6.63,
    "month": 1,
    "year": 2017
},
{
    "amount": 29.74,
    "month": 2,
    "year": 2017
},
{
    "amount":12.75,
    "month": 3,
    "year": 2017
},
{
    "amount": 0,
    "month": 1,
    "year": 2018
},
{
    "amount": 71.84,
    "month": 2,
    "year": 2018
},
{
    "amount": 26.62,
    "month": 3,
    "year": 2018
}]

我引用了这个例子:Group array items using object

但是我无法整理出求和部分，我得到的只是特定月份和年份的第一个值。

Answer 1

使用reduce、Object.values和sort

var fnGetKey = (obj) => JSON.stringify({year:obj.year, month:obj.month}); //get key from object
Object.values(arr.reduce( (a,c) => {
  var key = fnGetKey( c );
  !a[key] ? (a[key] = c) : (a[key].amount += c.amount); //Initialize with c if key doesn't exists in accumulator, else increment amount
  return a; //return accumulator
} ,{})).sort( (a,b) => a.year - b.year || a.month - b.month ); //sort by year and month

演示

var arr = [{
    "amount": 4.27,
    "month": 1,
    "year": 2017
  },
  {
    "amount": 2.46,
    "month": 1,
    "year": 2017
  },
  {
    "amount": 1.5,
    "month": 2,
    "year": 2017
  },
  {
    "amount": 28.24,
    "month": 2,
    "year": 2017
  },
  {
    "amount": 8.24,
    "month": 3,
    "year": 2017
  },
  {
    "amount": 3.65,
    "month": 3,
    "year": 2017
  },
  {
    "amount": 0.86,
    "month": 3,
    "year": 2017
  },
  {
    "amount": 0,
    "month": 1,
    "year": 2018
  },
  {
    "amount": 71.84,
    "month": 2,
    "year": 2018
  },
  {
    "amount": 26.62,
    "month": 3,
    "year": 2018
  }
];

var fnGetKey = (obj) => JSON.stringify({
  year: obj.year,
  month: obj.month
}); //get key from object


var output = Object.values(arr.reduce((a, c) => {
  var key = fnGetKey(c);
  !a[key] ? (a[key] = c) : (a[key].amount += c.amount);
  return a;
}, {})).sort((a, b) => a.year - b.year || a.month - b.month);

console.log(output);