add values and merge array in object?

Question

I want to create a new object by adding count values of keys with the same name
and then merge them.
I could use filter and map but that's for the case that I already know
what keys would be inside of the object. like below.

obArr.filter(v => v.site === 'jelly').map(...);

but it needs lot of works (lot of filter and map for each key) and
key name would be vary each time. In this case what could be the better way?
This is the data and desired result below.


const obArr = [{site: "candy", date: "2021-04-30", count: 10},
{site: "jelly", date: "2021-04-30", count: 2},
{site: "candy", date: "2021-04-29", count: 12},
{site: "jelly", date: "2021-04-29", count: 3},
{site: "candy", date: "2021-04-29", count: 5},
{site: "chocolate", date: "2021-04-29", count: 9},
{site: "jelly", date: "2021-04-29", count: 20},
{site: "chocolate", date: "2021-04-29", count: 21}];


//desired result
 const [state, setState] = useState([
    {site: 'candy', count: 27},
    {site: 'chocolate', count: 30},
    {site: 'jelly', count: '25'},
  ]);

CertainPerformance · Accepted Answer · 2021-04-30 05:11:33Z

1

Count up the number of counts on an object (or Map) instead while iterating over the array:

const obArr = [{site: "candy", date: "2021-04-30", count: 10},
{site: "jelly", date: "2021-04-30", count: 2},
{site: "candy", date: "2021-04-29", count: 12},
{site: "jelly", date: "2021-04-29", count: 3},
{site: "candy", date: "2021-04-29", count: 5},
{site: "chocolate", date: "2021-04-29", count: 9},
{site: "jelly", date: "2021-04-29", count: 20},
{site: "chocolate", date: "2021-04-29", count: 21}];

const grouped = {};
for (const { site, count } of obArr) {
  grouped[site] = (grouped[site] || 0) + count;
}
const initialState = Object.entries(grouped).map(([site, count]) => ({ site, count }));
console.log(initialState);

 // const [state, setState] = useState(initialState);

answered Apr 30, 2021 at 5:11

CertainPerformance

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1 Comment

bonlim Over a year ago

you are So genius

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