Lodash：组合数组 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

 var student = [{ 'id': 'xx001', 'code': 'taller', 'item': 2 },{ 'id': 'xx001', 'code': 'taller', 'item': 5 },{ 'id': 'xx002', 'code': 'small', 'item': 2 }]; let idList = Array.from(new Set(student.map(p => p.id))); console.log(idList); let result = []; idList.filter(p => { let filteredList = student.filter(k => p == k.id); console.log(filteredList); let itemList = filteredList.map(j => j.item); let sumItem = itemList.reduce((a, b) => a + b, 0); result.push({'id': p, 'code': filteredList[0].code, 'item': sumItem}); }) console.log(result);

This is result && i don't know what is the code so i ignored

Answer 2

Using _.reduce() , https://codepen.io/1010543618/pen/VwwgVwm?editors=0010

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

var result = _.reduce(student, function(res, stu, index, arr){
  var fstu = _.find(res, function(d){
    return d.id === stu.id;
  });
  if(fstu){
     fstu.item += stu.item;
  }else{
     res.push(_.clone(stu));
  }
  return res;
}, []);

console.log(result);

Answer 3

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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