How to create a unique array which has objects as elements?

Question

I have an array of students and I want to create an unique array of this students. Each student has a unique id value and I want to compare with this id value.

Here is a Student object;

{
    "id" = "3232aab1",
    //some other properties
}

*"...and I want to compare with this id value."* Okay. That seems like a good place ot start. Where are you stuck? What has your research shown you? What has [searching](/help/searching) turned up? — T.J. Crowder, Feb 07 '17 at 14:09
@hellzone: So the original can have students with the same id value? Do they have other properties? If so, how do you decide which one you want to keep? — Ry-, Feb 07 '17 at 14:14
@T.J.Crowder Actually I thought that Javascript can have an interface like Set in Java. — hellzone, Feb 07 '17 at 14:14
@hellzone: Yes, JavaScript has a `Set` type as of ES6. https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Set — Ry-, Feb 07 '17 at 14:16

score 2 · Accepted Answer · answered Feb 07 '17 at 14:12

var Students =[
{
    "id" : "3232aab1"  //some other properties
} ,
{
    "id" : "3232aab1"  //some other properties
}, 
{
    "id" : "3232aab2"  //some other properties
} ,
{
    "id" : "3232aab3"  //some other properties
} ,
{
    "id" : "3232aab2"  //some other properties
} ];

var tmpObj = {};
var uniqArray = Students.reduce(function(acc,curr){
  if (!tmpObj[curr.id]){
    tmpObj[curr.id] = true;
    acc.push(curr)
  }
  return acc;
},[]);
console.log(uniqArray);

score 0 · Answer 2 · edited Feb 07 '17 at 14:21

0

I'd probably take an approach similar to this...

class Students extends Map {
    set(key, value) {
        if (this.has(key)) { throw new Error('Student already there'); }
        return super.set(key, value);
    }
}


const students = new Students();

students.set(1, { name: 'Peter' });

console.log(students.get(1));

// students.set(1, { name: 'Gregor' }); this throws

edited Feb 07 '17 at 14:21

Ry-

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answered Feb 07 '17 at 14:13

Lyubomir

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Every value set in that map is going to be `undefined`. (didn’t downvote btw) – Ry- Feb 07 '17 at 14:15
1

This is over kill – Laazo Feb 07 '17 at 14:16
Java us not javascript. Check the tag – Sagar V Feb 07 '17 at 14:16
2

@SagarV: This *is* JavaScript. Try it. – Ry- Feb 07 '17 at 14:17
Ok. but he is not familiar with JS. and it is very tough for him. class and such things are new concepts to javascript – Sagar V Feb 07 '17 at 14:19

score 0 · Answer 3 · answered Feb 07 '17 at 14:15

var a=[];
a.push({id:1,name:"something"});
// repeat similar;

To access an id

a[index].id;

Sample code to search

var elem = 1; // id to be searched
//loop
for(var i=0; i<a.length; i++){
  if(elem == a[i].id){
    break;
  }
}
// now a[i] will return the required data {id:1,name:"something"}
// a[i].id = > 1 and a[i].name => something

score -1 · Answer 4 · answered Feb 07 '17 at 14:43

-1

If you have underscore, you can use the following

ES6 _.uniq(Students, student=>student.id)

ES5 _.uniq(Students, function(student){return student.id;})

answered Feb 07 '17 at 14:43

mdsAyubi

1,225
9
9

What if OP doesn't use underscore? OP didn't tag it so would be better if it was a plain JS answer. – putvande Feb 07 '17 at 14:48

How to create a unique array which has objects as elements?

4 Answers4