Select distinct object from a list without using foreach loop in angular

Question

I have a source list of objects of 4 properties with some duplicate values, want to select distinct objects of 2 properties without using a foreach loop.

Source list:

let Students=  [
 {Id: 1, Name: 'A', Class: 'I', Subject: 'Math'},
 {Id: 2, Name: 'B', Class: 'II', Subject: 'Bengali'},
 {Id: 1, Name: 'A', Class: 'I', Subject: 'Science'},
 {Id: 2, Name: 'B', Class: 'II', Subject: 'English'}
];

I want an output list like:

[
  {Id: 1, Name: 'A'},
  {Id: 2, Name: 'B'}
]

Take a look to [this](https://www.learnrxjs.io/operators/transformation/groupby.html). — dcg, Jun 22 '19 at 04:41
Did any answer work for you? If yes do consider accepting/upvoting one [What should I do when someone answers my question?](https://stackoverflow.com/help/someone-answers) — Nicholas K, Jun 26 '19 at 13:51

Nicholas K · Answer 1 · 2019-06-24T07:02:46.597

Since we're in the world of typescript, make use of the types provided by it. Create a class Student, this will be useful for easier management of your objects.

export class Student {
  Id: number;
  Name: string;
  Class?: string;
  Subject?: string;

  constructor(Id: number, Name: string) {
    this.Id = Id;
    this.Name = Name;
  }
}

Create an array to hold the distinct objects:

distinctStud: Student[] = [];

Now you may:

from(this.Students)
   .pipe(
      map(std => new Student(std.Id, std.Name)),
      distinct(x => x.Id && x.Name)
    )
   .subscribe(val => this.distinctStud.push(val));

score 1 · Accepted Answer · answered Nov 14 '19 at 07:25

1

Simple Solution to return Distinct data for Object Array

this.studentOptions = this.students.filter((item, i, arr) => arr.findIndex((t) => t.Id=== item.Id) === i);

answered Nov 14 '19 at 07:25

Dhruv Parekh

156
1
5

score 0 · Answer 3 · answered Jun 22 '19 at 05:53

0

Array.from(new Set(yourArray.map((item: any) => item.id)))

answered Jun 22 '19 at 05:53

Ali Siahmansouri

1

score 0 · Answer 4 · answered Jun 22 '19 at 05:59

0

You can try this like newbie way

    let st=[];
Students.map((data)=>{
 let isExist=!!st.find((data2)=>{ 
 return data2.Id==data.Id});
if(!isExist)
  st.push(data);
});

answered Jun 22 '19 at 05:59

Shahid Islam

440
3
6

score 0 · Answer 5 · answered Jun 22 '19 at 11:00

Using rxjs's map and distinct operators we can achieve this. Please check the code below

   var Students=  [
 {Id: 1, Name: 'A', Class: 'I', Subject: 'Math'},
 {Id: 2, Name: 'B', Class: 'II', Subject: 'Bengali'},
 {Id: 1, Name: 'A', Class: 'I', Subject: 'Science'},
 {Id: 2, Name: 'B', Class: 'II', Subject: 'English'}
];

  const sourceObj = from(Students);
  const mappedObj=sourceObj.pipe(map((x)=>{return {Id: x.Id, Name:x.Name}}));
  const distictObj = mappedObj.pipe(distinct((x)=>x.Id && x.Name));

  console.log(distictObj.subscribe(x=>console.log(x)));

Please check this StackBlitz.

Thanks.

uminder · Answer 6 · 2019-06-22T14:40:55.510

This solution produces the result in the form you asked for. Objects need to be stringified before they get added to the Set, otherwise equal ones are not recognized (see https://stackoverflow.com/a/29759699/2358409).

const set = new Set(Students.map(s => JSON.stringify({ Id: s.Id, Name: s.Name })));
const identifiers = Array.from(set).map(i => JSON.parse(i));

If you want to avoid stringify, you can do the following.

const set = new Set(Students.map(s => s.Id + ';' + s.Name));
const identifiers = Array.from(set).map(i => ({ Id: i.split(';')[0], Name: i.split(';')[1] }));

The same can be done in a cleaner way using Map.

const map = new Map();
Students.map(s => map.set(s.Id, { Id: s.Id, Name: s.Name }));
const identifiers = Array.from(map.values());

Select distinct object from a list without using foreach loop in angular

6 Answers6