How to group array of objects?

Question

I have an array of objects such as:

const array = [
  {
    date: '02-02-1994',
    time: '18:00',
    services: {
      first: 1,
      second: 1
    }
  },
  {
    date: '02-02-1994',
    time: '20:00',
    services: {
      first: 1,
      second: 1
    }
  },
  {
    date: '02-04-1994',
    time: '19:00',
    services: {
      first: 1,
      second: 1
    }
  },
{
  date: '02-04-1994',
  time: '19:00',
  services: {
    first: 1,
    second: 2
  }
}
]

I want to group it by time and date and get the result array:

const result = [{
  date: '02-02-1994',
  time: '18:00',
  services: {
    first: 1,
    second: 1
  }
},
{
  date: '02-02-1994',
  time: '20:00',
  services: {
    first: 1,
    second: 1
  }
},
{
  date: '02-04-1994',
  time: '19:00',
  services: {
    first: 2,
    second: 3
  }
}]

I want to group array by date then by time and to get a sum in service object. I try to group by date using reduce, but then I don't know

I grouped by date jsfiddle.net/atcr04vm But then I don't know... — work-react
– work-react, Commented Sep 10, 2019 at 20:55

Nikhil · Accepted Answer · 2019-09-10 21:29:04Z

1

You can use reduce() method to do that.

const array = [{ date: '02-02-1994', time: '18:00', services: { first: 1, second: 1 } }, { date: '02-02-1994', time: '20:00', services: { first: 1, second: 1 } }, { date: '02-04-1994', time: '19:00', services: { first: 1, second: 1 } }, { date: '02-04-1994', time: '19:00', services: { first: 1, second: 2 } } ];

let result = array.reduce((arr, currentValue) => {

  let item = arr.find(item =>
    item.date === currentValue.date &&
    item.time === currentValue.time);

  if (item) {
    item.services.first += currentValue.services.first;
    item.services.second += currentValue.services.second;
  } else {
    arr.push(currentValue);
  }

  return arr;
}, []);

console.log(result);

answered Sep 10, 2019 at 21:29

Nikhil

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Comments

Nina Scholz · Accepted Answer · 2019-09-10 20:59:58Z

You could take a joined key for collecting items of the same group in an object and then take the values of it as result set.

var array = [{ date: '02-02-1994', time: '18:00', services: { first: 1, second: 1 } }, { date: '02-02-1994', time: '20:00', services: { first: 1, second: 1 } }, { date: '02-04-1994', time: '19:00', services: { first: 1, second: 1 } }, { date: '02-04-1994', time: '19:00', services: { first: 1, second: 2 } }],
    result = Object.values(array.reduce((r, { date, time, services }) => {
        var key = [date, time].join('|');
        r[key] = r[key] || { date, time, services: {} };
        Object
            .entries(services)
            .forEach(([k, v]) => r[key].services[k] = (r[key].services[k] || 0) + v);
        return r;
    }, {}));

   console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

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