Lodash: Combine array object

Question

I want to combine the array with same id for example

var student = [{
   'id': 'xx001',
   'code': 'taller',
   'item': 2,
   'date': '2019-01-01'
},{
   'id': 'xx001',
   'code': 'taller',
   'item': 5,
   'date': '2019-01-01'
},{
   'id': 'xx001',
   'code': 'taller',
   'item': 5,
   'date': '2019-03-24'
},{
   'id': 'xx002',
   'code': 'small',
   'item': 2,
   'date': '2019-01-01'
}]

and the output should be.

and when it combine the same id it will added the item and if the date is not the same it should seperate.

Answer 1

Don't really need lodash, but since it's asked for you can loop using _.forEach and then check if we already have the item using _.find()

Snippet I have also included a non-lodash version:

var students = [{
  'id': 'xx001',
  'code': 'taller',
  'item': 2
}, {
  'id': 'xx001',
  'code': 'taller',
  'item': 5
}, {
  'id': 'xx002',
  'code': 'small',
  'item': 2
}];

const output = [];
_.each(students, x => {
  const existing = _.find(output, {
    id: x.id
  });

  if (existing) {
    existing.item += x.item;
  } else {
    output.push(x);
  }
});

console.info(output);

const students2 = [{
  'id': 'xx001',
  'code': 'taller',
  'item': 2
}, {
  'id': 'xx001',
  'code': 'taller',
  'item': 5
}, {
  'id': 'xx002',
  'code': 'small',
  'item': 2
}];

const output2 = [];
students2.forEach(x => {
  const existing = output2.find(y => y.id === x.id);

  if (existing) {
    existing.item += x.item;
  } else {
    output2.push(x);
  }
});

console.log(output2);


var students3 = [{
   'id': 'xx001',
   'code': 'taller',
   'item': 2,
   'date': '2019-01-01'
},{
   'id': 'xx001',
   'code': 'taller',
   'item': 5,
   'date': '2019-01-01'
},{
   'id': 'xx001',
   'code': 'taller',
   'item': 5,
   'date': '2019-03-24'
},{
   'id': 'xx002',
   'code': 'small',
   'item': 2,
   'date': '2019-01-01'
}]

const output3 = [];
students3.forEach(x => {
  const existing = output3.find(y => y.id === x.id && y.date === x.date);

  if (existing) {
    existing.item += x.item;
  } else {
    output3.push(x);
  }
});

console.log(output3);

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