Typescript reduce object array by specific value

Question

I have this:

0: {orderType: "orderType1", orderCount: 0, orderDate: 47}
1: {orderType: "orderType1", orderCount: 21, orderDate: 47}
2: {orderType: "orderType1", orderCount: 3, orderDate: 47}
3: {orderType: "orderType1", orderCount: 5, orderDate: 48}
4: {orderType: "orderType1", orderCount: 32, orderDate: 48}
5: {orderType: "orderType1", orderCount: 12, orderDate: 48}

and I would like to achieve this:

0: {orderType: "orderType1", orderCount: 24, orderDate: 47}
1: {orderType: "orderType1", orderCount: 49, orderDate: 48}

Basically I want to 'combine' or 'reduce' the entries by combining the orderCount based on orderDate.

Apologies if combine or reduce are not the right terms here.

For future readers, this is basically a duplication of this question: https://stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-an-array-of-objects check out the answer there for a cleaner solution — Tal Joffe, Dec 27 '21 at 13:00

score 6 · Accepted Answer · answered Nov 27 '18 at 11:12

Someone smarter than me can probably do this more succinctly, but if I group the data and then reduce it I can get the desired result.

I have a feeling this could be done in fewer steps:

function setFilter(value, index, self) { 
    return self.indexOf(value) === index;
}

function groupBy(objectArray, property) {
  return objectArray.reduce(function (acc, obj) {
    var key = obj[property];
    if (!acc[key]) {
      acc[key] = [];
    }
    acc[key].push(obj);
    return acc;
  }, {});
}

const data = [
    { orderType: "orderType1", orderCount: 0, orderDate: 47 },
    { orderType: "orderType1", orderCount: 21, orderDate: 47 },
    { orderType: "orderType1", orderCount: 3, orderDate: 47 },
    { orderType: "orderType1", orderCount: 5, orderDate: 48 },
    { orderType: "orderType1", orderCount: 32, orderDate: 48 },
    { orderType: "orderType1", orderCount: 12, orderDate: 48 }
];

const groupedData = groupBy(data, 'orderDate');
const reducedData = [];

for (let key in groupedData) {
    let initialValue = 0;
    let sum = groupedData[key].reduce((accumulator, currentValue) => {
        return accumulator + currentValue.orderCount;
    },initialValue)

    reducedData.push({
        orderType: groupedData[key][0].orderType,
        orderCount: sum,
        orderDate: key
    });
}

console.log(reducedData);

This doesn't take into account orderType and I feel it ought to.

Worked like a charm. orderType can be omitted,, it's being filtered on an upper level. I've made small adjustment here: `for (let key in groupedData) {` changed to `for (const key of Object.keys(groupedData)) {` Thank you very much! — ZGanchev, Nov 27 '18 at 11:38

score 1 · Answer 2 · answered Nov 27 '18 at 14:58

Here is a (slightly) shorter version also using reduce :

 const data = [
    { orderType: "orderType1", orderCount: 0, orderDate: 47 },
    { orderType: "orderType1", orderCount: 21, orderDate: 47 },
    { orderType: "orderType1", orderCount: 3,  orderDate: 47 },
    { orderType: "orderType1", orderCount: 5,  orderDate: 48 },
    { orderType: "orderType1", orderCount: 32, orderDate: 48 },
    { orderType: "orderType1", orderCount: 12, orderDate: 48 }];

let foundIdx;

var result = data.reduce((accu, curr, idx, arr) => {
    if (accu.some((value, resIdx, reArr) => {  // present in out array?
        foundIdx = resIdx;        
        return (value.orderType == curr.orderType && value.orderDate == curr.orderDate);
    }))
    {    // already present, increment OrderCount
        accu[foundIdx].orderCount += curr.orderCount;
    }
    else {   // not yet present push the element
        accu.push(curr);
    }
    return accu;
}, []);

console.log(JSON.stringify(result));
//[{"orderType":"orderType1","orderCount":24,"orderDate":47},{"orderType":"orderType1","orderCount":49,"orderDate":48}]

Typescript reduce object array by specific value

2 Answers2