获取具有平均值的对象数组的重复计数

Question

I Have a dataset that looks like this:

var arr = [
  { userid: "5bacc98431481e0520856df8", profitLoss: 401.4 },
  { userid: "5bacc98431481e0520856df8", profitLoss: -28.36 },
  { userid: "5bacc8c6563a882a1ca7756a", profitLoss: -26.14 },
  { userid: "5bacc8c6563a882a1ca7756a", profitLoss: 46.14},
  { userid: "5bacc8c6563a882a1ca7756a", profitLoss: 86.14}
];

Now I want the repetition count of userid with average value of profitLoss.

Expected result will be like this:
var arr = [
  { userid: "5bacc98431481e0520856df8", profitLoss: 186.52, count: 2 },
  { userid: "5bacc8c6563a882a1ca7756a", profitLoss: 106.14, count: 3}
];

I know to get the repetition count of array but not on object; for repetition count of array the logic will be like this:

var map = arr.reduce(function(prev, cur) {
  prev[cur] = (prev[cur] || 0) + 1;
  return prev;
}, {});

But I am confused on array of objects.

Answer 1

You could take a Map and sum the values an count. Later get the average.

 var array = [{ userid: "5bacc98431481e0520856df8", profitLoss: 401.4 }, { userid: "5bacc98431481e0520856df8", profitLoss: -28.36 }, { userid: "5bacc8c6563a882a1ca7756a", profitLoss: -26.14 }, { userid: "5bacc8c6563a882a1ca7756a", profitLoss: 46.14 }, { userid: "5bacc8c6563a882a1ca7756a", profitLoss: 86.14 }], result = Array.from( array.reduce((m, { userid, profitLoss }) => { var temp = m.get(userid) || { sum: 0, count: 0 }; temp.sum += profitLoss; temp.count++; return m.set(userid, temp); }, new Map), ([userid, { sum, count }]) => ({ userid, average: sum / count, count }) ); console.log(result); 

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Answer 2

You could create dictionary with userid as key and object with sum and count. Then it's enough to map entries to your result.

 var arr = [ { userid: "5bacc98431481e0520856df8", profitLoss: 401.4 }, { userid: "5bacc98431481e0520856df8", profitLoss: -28.36 }, { userid: "5bacc8c6563a882a1ca7756a", profitLoss: -26.14 }, { userid: "5bacc8c6563a882a1ca7756a", profitLoss: 46.14}, { userid: "5bacc8c6563a882a1ca7756a", profitLoss: 86.14} ]; var userDict = arr.reduce((acc, el)=>{ if (!acc.hasOwnProperty(el.userid)){ acc[el.userid] = {sum: 0, count: 0} } acc[el.userid].sum += el.profitLoss; acc[el.userid].count++; return acc; }, {}); var result = Object.entries(userDict).map(([k,v])=>({userid: k, average: v.sum/v.count, count:v.count})); console.log(result)