Get array of student's id

Question

Help me get the array of all student's id and college id from the following JSON data. I want to have;

//to store id of all colleges.
var collegeid = [];

//store id of all students.
var studentsid = [];

//students id as per college:
var studentsIdInCollege1 = [];

var data = {  
  "college":[  
    {  
      "id":1,
      "school":"abc",
      "course":"cde",
      "students":[  
        {  
          "id":1,
          "name":"abc 123",
          "number":"156888"
        },
        {  
          "id":2,
          "name":"abc 123",
          "number":"156888"
        }
      ]
    },
    {  
      "id":2,
      "school":"xyz",
      "course":"lopl",
      "students":[  
        {  
          "id":3,
          "name":"abc 123",
          "number":"156888"
        },
        {  
          "id":4,
          "name":"abc 123",
          "number":"156888"
        }
      ]
    }
  ]
}

`

Possible duplicate of [How to convert JSON object to an Typescript array?](https://stackoverflow.com/questions/39308423/how-to-convert-json-object-to-an-typescript-array) - there are some other duplicates around. — kabanus, Apr 28 '18 at 07:34
Possible duplicate of [Access / process (nested) objects, arrays or JSON](https://stackoverflow.com/questions/11922383/access-process-nested-objects-arrays-or-json) — JJJ, Apr 28 '18 at 07:46

score 2 · Answer 1 · answered Apr 28 '18 at 07:39

2

For the colleges, just map the college array to the id of each object. For the students, use [].concat(... to spread over a map of the student IDs and get a flat object:

const input = {  
  "college":[  
    {  
      "id":1,
      "school":"abc",
      "course":"cde",
      "students":[  
        {  
          "id":1,
          "name":"abc 123",
          "number":"156888"
        },
        {  
          "id":2,
          "name":"abc 123",
          "number":"156888"
        }
      ]
    },
    {  
      "id":2,
      "school":"xyz",
      "course":"lopl",
      "students":[  
        {  
          "id":3,
          "name":"abc 123",
          "number":"156888"
        },
        {  
          "id":4,
          "name":"abc 123",
          "number":"156888"
        }
      ]
    }
  ]
}

const collegeIds = input.college.map(({ id }) => id);
console.log('collegeIds: ' + collegeIds);
const studentIds = [].concat(...input.college.map(({ students }) => students.map(({ id }) => id)));
console.log('studentIds: ' + studentIds);

answered Apr 28 '18 at 07:39

CertainPerformance

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Thanks!. How can i get students id only for specific college. say college with id of 1. – 7guyo Apr 28 '18 at 07:44
You would select the appropriate college using `.find` and then use the same sort of `map` technique as with collegeIds over the students to get their ids. – CertainPerformance Apr 28 '18 at 07:46
Hi @CertainPerformance, i love your code , i dont understant this [].concat(...input.college.map(({ students }), three dots in concat – jvk Apr 28 '18 at 08:07
Am having difficulty in putting the ids in array, as; collegeIds: [1,2] I tried `collegeIds[]=collegeIds.push(input.college.map(({ id }) => id));` – 7guyo Apr 28 '18 at 08:59
@7guyo Don't put empty square brackets after variable names - it's invalid syntax. Do ``const college = input.college.find(({ id }) => id === 1); const studentIds = college.students.map(({ id }) => id);`` – CertainPerformance Apr 28 '18 at 09:13
@whoami Spread operator. It's a quick way of flat-mapping one level deep. – CertainPerformance Apr 28 '18 at 09:14

Mohammad Usman · Accepted Answer · 2018-04-28T07:54:46.477

Use .map() to get college Ids:

let collegeIds = data.college.map(({ id }) => id);

Use .reduce() for student ids:

let studentIds = data.college.reduce((a, c) => (
  a.concat(c.students.map(({ id }) => id))
), []);

Use .reduce() to get an array of arrays where each array contains student ids:

let studentInEachCollege = data.college.reduce((a, c) => (
  a.push(c.students.map(({ id }) => id)), a
), []);

This will allow you to access each college students using index like studentInEachCollege[0] for first college, studentInEachCollege[1] for second and so on.

Demo:

var data = {  
  "college":[  
    {  
      "id":1,
      "school":"abc",
      "course":"cde",
      "students":[  
        {  
          "id":1,
          "name":"abc 123",
          "number":"156888"
        },
        {  
          "id":2,
          "name":"abc 123",
          "number":"156888"
        }
      ]
    },
    {  
      "id":2,
      "school":"xyz",
      "course":"lopl",
      "students":[  
        {  
          "id":3,
          "name":"abc 123",
          "number":"156888"
        },
        {  
          "id":4,
          "name":"abc 123",
          "number":"156888"
        }
      ]
    }
  ]
};

let collegeIds = data.college.map(({ id }) => id);
let studentIds = data.college.reduce((a, c) => (
  a.concat(c.students.map(({ id }) => id))
), []);
let studentInEachCollege = data.college.reduce((a, c) => (
  a.push(c.students.map(({ id }) => id)), a
), []);

console.log(collegeIds);
console.log(studentIds);
console.log(studentInEachCollege);

Docs:

score 1 · Answer 3 · answered Apr 28 '18 at 07:42

// College ids 
var cID = data.college.map((c) => { return c.id});

// Students
// It returns two arrays so you need to reduce it...
var students = data.college.map((c) => { return c.students});

var allStudents = students.reduce((a,b) => {return a.concat(b)}, []);

// IDs
var sID = allStudents.map((c) => { return c.id});

Get array of student's id

3 Answers3