Construct new array of objects based on existing array and object

Question

Probably making a silly mistake, but i can't seem to figure this one out.

Based on an existing array of strings, i want to check if they exist as an object value within my array of objects. If true, push them into the new array with a true value, if false, also push them in the new array, but with a false value.

Example of my code so far:

const answers = [12, 3, 16]
const quotes = [
{ id: 12, author: 'A'}, 
{ id: 4, author: 'B'}, 
{ id: 16, author: 'C'},  
]

let checkedQuotes = [];

answers.forEach((answer) => {
   quotes.find((quote) => (quote.id === answer
       && checkedQuotes.push({
         id: quote.id,
         author: quote.author,
         correct: true,
       })
   ));
 });

returns => [
  {id:12, author: 'A', correct: true}, 
  {id:16, author: 'C', correct: true}
]

This pushes objects to my new array, and it all works fine! Problem is when i want to add the false ones. I'm trying to do this as followed:

answers.forEach((answer) => {
    quotes.find((quote) => (quote.id === answer
      ? checkedQuotes.push({
        id: quote.id,
        author: quote.author,
        correct: true,
      })
      : checkedQuotes.push({
        id: quote.id,
        author: quote.author,
        correct: false,
      })
    ));
  });

returns => [
  {id:12, author: 'A', correct: true}, 
  {id:12, author: 'A', correct: false}, 
  {id:12, author: 'A', correct: false}
]

// would expect it to be: 
[
  {id:12, author: 'A', correct: true}, 
  {id:4, author: 'B', correct: false}, 
  {id:16, author: 'C', correct: true}
]

What am i missing here?

Ben Stephens · Accepted Answer · 2021-05-21 18:48:06Z

1

I think that you need to be looping through quotes rather than answers, and then seeing if there's a matching value for the quote in the answers.

const answers = [12, 3, 16];
const quotes = [
  { id: 12, author: 'A' }, 
  { id: 4, author: 'B' }, 
  { id: 16, author: 'C' },  
];

const res = quotes.map(
  (quote) => ({ ...quote, correct: answers.includes(quote.id) })
);

console.log(res);

answered May 21, 2021 at 18:48

Ben Stephens

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Comments

Rickard Elimää · Accepted Answer · 2021-05-21 19:01:47Z

Here is an answer for a minimal amount of loops.

Create an object from the answer array - {'value': true}, using reduce.
Looping through the answers, while checking up if the answer is correct in the object that is created in point 1).

const answers = [12, 3, 16]
const quotes = [
{ id: 12, author: 'A'}, 
{ id: 4, author: 'B'}, 
{ id: 16, author: 'C'},  
]

const answersObj = answers.reduce(function(obj, answer) {
  obj[answer] = true;
  return obj;
}, {});

for (quote of quotes) {
  quote['correct'] = answersObj[quote.id] || false;
}

console.log(quotes)

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