Getting duplicate objects out from my array in TypeScript

Question

I have an array of objects in my TypeScript-code and I need to get out the duplicate ones. The following code does the work for me:

 const uniqueObjects = Array.from(new Set(nonUniqueObjects.map((x) => {
        return JSON.stringify(x);
      }))).map((y) => JSON.parse(y));

The problem is when I run the code I get an error from Awesome TypeScript loader which is the following

Argument of type '{}' is not assignable to parameter of type 'string'.

The code which it doesn't probably like is the .map((y) => JSON.parse(y));

I also want to achieve this without using var or let, only const.

Jeremy Thille · Accepted Answer · 2017-08-09 13:36:05Z

1

Try with the spread operator :

let nonUniqueObjects = [{a : 1} , {b : 2}, {a : 1}, {b : 2}, {c : 3}]

const uniqueObjects = [...new Set(nonUniqueObjects.map( x => JSON.stringify(x)))]
		     .map( y => JSON.parse(y) )

console.log(uniqueObjects)

answered Aug 9, 2017 at 13:36

Jeremy Thille

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1 Comment

user2515670 Over a year ago

Still getting the same error. I'm pretty sure it has something to do with TypeScript, since this works perfectly in javascript

user2515670 · Accepted Answer · 2017-08-10 08:09:30Z

Found the solution. The problem was with

.map((y) => JSON.parse(y));

My TypeScript compiler didn't seem to like that 'y' wasn't a string, even though it made it into a string. So I solved it by calling toString().

.map((y) => JSON.parse(y.toString()));

The complete solution for removing non-unique Objects in an array:

  const uniqueObjects = Array.from(new Set(nonUniqueObjects.map((x) => JSON.stringify(x)))).map((y) => JSON.parse(y.toString()));

Probably still need to do some error handling, but that's a different story.

FAISAL · Accepted Answer · 2017-08-09 13:59:42Z

0

Here,

var nonUniqueObjects = [{
  'id': 1,
  'name': 'A'
}, {
  'id': 2,
  'name': 'B'
}, {
  'id': 1,
  'name': 'A'
}];

var uniqueObjects = new Set();
nonUniqueObjects.forEach(e => uniqueObjects.add(JSON.stringify(e)));
uniqueObjects = Array.from(uniqueObjects).map(e => JSON.parse(e));

console.log(JSON.stringify(uniqueObjects));

var uniqueObjects = new Set();
nonUniqueObjects.forEach(e => uniqueObjects.add(JSON.stringify(e)));
uniqueObjects = Array.from(uniqueObjects).map(e => JSON.parse(e));

edited Aug 9, 2017 at 13:59

answered Aug 9, 2017 at 13:47

FAISAL

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5 Comments

user2515670 Over a year ago

I should have mentioned, but I'm trying to do this without using var or let

FAISAL Over a year ago

that is only to show an example. See the updated answer with code.

user2515670 Over a year ago

If uniqueObjects is a const, then you can't assign the Array.from-part to it. You would just end up with 'Uncaught TypeError: Assignment to constant variable.'

FAISAL Over a year ago

you dont need it as a const.

user2515670 Over a year ago

Sorry, but the fact just is that I can only use Const and I know it's doable

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