How to group array items by multiple properties and sum groups?

Question

with underscore, I have successfully implemented the logic to group objects by multiple properties and sum the groups, but I haven't found the way to do it with lodash.

Here is the code:

let test = _.chain(response.counterValues)
  .flatten()
  .groupBy(response.counterValues, (item) => {
      return item.duration + '#' + item.timeFrom + '#' + item.timeTo + '#' + item.objectClass;
  })
  .mapValues((value, key) => {
    let sum = _.reduce(value, (memo, val) => {return memo + val.count}, 0);
    let keyItems = key.split('#');
    let duration = keyItems[0];
    let timeFrom = keyItems[1];
    let timeTo = keyItems[2];
    let objectClass = keyItems[3];
    return {duration: duration, timeFrom: timeFrom, timeTo: timeTo, objectClass: objectClass, count: sum};
  }).value();
console.log(test);

and these are example values:

0: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 1}
1: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 3}
2: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 1}
3: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 1}
4: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 3}
5: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 2}
6: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 1}
7: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 2}
8: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 4}
9: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 1}
10: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 2}
11: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 2}
12: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 2}
13: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 3}
14: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 2}
15: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 1}
16: {duration: "h", timeFrom: "1547323200000", timeTo: "1547326800000", objectClass: "car", count: 1}

For these objects, I would like to get the following result:

{duration: "h", timeFrom: 1547323200000, timeTo: 1547326800000, objectClass: "car", count: 32}

Does anyone know how to modify the code above in order to get the desired result?

Without actual code I was wondering why you want to stick to lodash in the first place. I'd most likely use Array.reduce and dynamically build the resulting object. To add more details: Most likely I'd use Array.reduce to return a Record<GroupType, ResultType> and either add a new element to the Record or updating the existing element while looping through the initial array. — Christian Ivicevic
– Christian Ivicevic, Commented Jan 12, 2019 at 23:55
Does the output must have timeFrom the min time from and timeTo the max or it's irrelevant since each item has them equal? — edin-m
– edin-m, Commented Jan 12, 2019 at 23:59

edin-m · Accepted Answer · 2019-01-13 00:14:48Z

1

.groupBy(response.counterValues, (item) => { ...

should be

.groupBy((item) => { ...

because you're using _.chain()

answered Jan 13, 2019 at 0:14

edin-m

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