Sum of array object for previous dates

Question

Origin Object is:

obj = { date: '2021-05-30', stock: 230, location_id: 'Bangalore' },
{ date: '2021-05-31', stock: 350, location_id: 'Bangalore' },
{ date: '2021-06-01', stock: 320, location_id: 'Bangalore' },
{ date: '2021-06-07', stock: 210, location_id: 'Bangalore' },
{ date: '2021-06-08', stock: 210, location_id: 'Bangalore' },
{ date: '2021-06-09', stock: 210, location_id: 'Bangalore' },
{ date: '2021-06-10', stock: 210, location_id: 'Bangalore' },
]
obj.reduce((m, o, i) => {
  var prev = m[i - 1];
  if (prev) {
    o.stock = o.stock + prev.stock;
  }
  m.push(o);
  return m;
}, []);

I tried above script but is updating current date itself. But I am getting following outcome:

0: {date: "2021-05-31", stock: 230, location_id: "Bangalore"}
1: {date: "2021-05-31", stock: 580, location_id: "Bangalore"}
2: {date: "2021-06-01", stock: 900, location_id: "Bangalore"}
3: {date: "2021-06-07", stock: 1110, location_id: "Bangalore"}
4: {date: "2021-06-08", stock: 1320, location_id: "Bangalore"}
5: {date: "2021-06-09", stock: 1530, location_id: "Bangalore"}
6: {date: "2021-06-10", stock: 1740, location_id: "Bangalore"}```

Expecting format is like

0: {date: "2021-05-30", stock: 0, location_id: "Bangalore"}
1: {date: "2021-05-31", stock: 230, location_id: "Bangalore"}
2: {date: "2021-06-01", stock: 580, location_id: "Bangalore"}
3: {date: "2021-06-07", stock: 900, location_id: "Bangalore"}
4: {date: "2021-06-08", stock: 1110, location_id: "Bangalore"}
5: {date: "2021-06-09", stock: 1320, location_id: "Bangalore"}
6: {date: "2021-06-10", stock: 1530, location_id: "Bangalore"}```

Please anyone provide the right solution is greatly appreciated!

bel3atar · Accepted Answer · 2021-05-30 12:24:07Z

1

const obj = [
  { date: '2021-05-30', stock: 230, location_id: 'Bangalore' },
  { date: '2021-05-31', stock: 350, location_id: 'Bangalore' },
  { date: '2021-06-01', stock: 320, location_id: 'Bangalore' },
  { date: '2021-06-07', stock: 210, location_id: 'Bangalore' },
  { date: '2021-06-08', stock: 210, location_id: 'Bangalore' },
  { date: '2021-06-09', stock: 210, location_id: 'Bangalore' },
  { date: '2021-06-10', stock: 210, location_id: 'Bangalore' },
]
obj.reduce((acc, cur) => { 
  const newAcc = acc + cur.stock; 
  cur.stock = acc; 
  return newAcc 
},0)
console.log(obj)

answered May 30, 2021 at 12:24

bel3atar

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