Angular 4 GroupBy Array Data

Question

I have an array which looks like:

var data = [
  {
    student: "sam",
    English: 80,
    Std: 8
  },
  {
    student: "sam",
    Maths: 80,
    Std: 8
  },
  {
    student: "john",
    English: 80,
    Std: 8
  },
  {
    student: "john",
    Maths: 80,
    Std: 8
  }
];

and I need to get the total marks irrespective of subject for student sam.

By filtering data array by student name and then looping the filtered data, can get the individual student total marks.

Is there any groupBy function as similar to SQL in Typescript.

Is https://stackoverflow.com/a/34890276/7124761 what you looking for? — Prashant Pimpale, Oct 10 '18 at 11:24
do you want something like this {student:"sam", English: 80, Maths: 80, Std: 8},{student:"john", English: 80, Maths, Std: 8}, — Asanka, Oct 10 '18 at 11:24
what is std? there is only 3 fields student,subject and std? — Asanka, Oct 10 '18 at 11:32
std- in what standard the student i studying. Yes there is only 3 fields — anand, Oct 10 '18 at 11:47
this is working but don't know if is what you want.. [link](https://stackblitz.com/edit/angular-r5xfyz?file=src%2Fapp%2Fhello.component.ts) — lesiano, Oct 10 '18 at 13:20

joshvito · Accepted Answer · 2018-10-11T16:18:58.063

This seems like it can be done with a simple reduce method on the array. Reduce will iterate over an array and pass each item into the provided predicate function. Each iteration should return the accumulator obj/array/val.

I wasn't sure what you wanted the data structure to be, but you can control the structure by the inner working of the function you pass to reduce.

  studentScores = this.data.reduce((accumulator, item) => {
    const key = Object.keys(item)
      .filter(k => k !== 'student')
      .filter(k => k !== 'Std')[0];
    const prevValue = accumulator[item.student] || 0;
    const studentName = item.student;
    accumulator[studentName] = prevValue + item[key];
    return accumulator;
  }, {});

I posted a working example in a stackblitz at https://stackblitz.com/edit/angular-xcjzzf

score -2 · Answer 2 · answered Oct 10 '18 at 15:54

-2

You have to do it using dictionary. Easy way to grouping is used a map.there mark's name is changing so the task is difficult.This is stackblitz link.

answered Oct 10 '18 at 15:54

Asanka

1,628
1
10
20

linked solution can become outdated. You should post reason and example in your answer too. – joshvito Oct 11 '18 at 16:20
thanks for the down vote. you can see my answer. that's why I post stackBlitz – Asanka Oct 11 '18 at 16:22

Angular 4 GroupBy Array Data

2 Answers2