converting two-dimensional array into array object in JavaScript

Question

I have following two-dimensional array code

var questions = [
  ['How many states are in the United States?', 50],
  ['How many continents are there?', 7],
  ['How many legs does an insect have?', 6]
];

and converted version of it to array object

var questions = [
 { question: 'How many states are in the United States?', answer: 50 },
 { question: 'How many continents are there?', answer: 7 },
 { question: 'How many legs does an insect have?', answer: 6 }
];

and have corresponding for loops.

for (var i = 0; i < questions.length; i += 1) {
    question = questions[i][0];
    answer = questions[i][1];
    response = prompt(question);
    response = parseInt(response);
if (response === answer) {
   correctAnswers += 1;
   correct.push(question);
  } else {
   wrong.push(question);
 }
}

and

  for (var i = 0; i < questions.length; i += 1) {
      question = questions[i].question;
      answer = questions[i].answer;
      response = prompt(question);
      response = parseInt(response);
  if (response === answer) {
    correctAnswers += 1;
  } 
}

What is the actual difference between two-dimensional array and array object? Would it affect running for loop faster to sort data ? How would I know which one is better ?

That's a terrible way to use arrays. questions[i][1] what is that? questions[i].answer actually makes sense. — Farzher
– Farzher, Commented Apr 16, 2015 at 4:39
it targets answer element. The task is to answer quiz questions... learning JavaScript and it was mentioned — user4530879
– user4530879, Commented Apr 16, 2015 at 4:40

Raos · Accepted Answer · 2020-04-08 01:47:02Z

2

Here is a solution in es6:

var questions = [
  ['How many states are in the United States?', 50],
  ['How many continents are there?', 7],
  ['How many legs does an insect have?', 6]
];
let keys = ["question", "answer"];
let result = questions.map(r => (keys.reduce((o, k, i) => (o[k] = r[i], o), {})));
console.log(result)

answered Apr 8, 2020 at 1:47

Raos

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Comments

Dylan Watt · Accepted Answer · 2015-04-16 05:34:07Z

1

The difference between the two depends a lot on the environment that the Javascript is being run in. Lets just see:

http://jsperf.com/array-vs-object-lookup-986

Running that in chrome V8, you can see the difference is notable, with a edge to a map lookup. The map lookup notation is also vastly more maintainable for future devs who have to work on your code.

Edit: The map way is 5x faster FF.

edited Apr 16, 2015 at 5:34

answered Apr 16, 2015 at 4:49

Dylan Watt

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Comments

nderscore · Accepted Answer · 2015-04-16 04:48:22Z

0

Functionally, there is not much difference. Arrays are just a special type of Object. Each index in the array is just a property of that object. So, a two-dimensional array is still an array of objects.

Performance-wise, you shouldn't see any noticeable impact either way.

In regards to readability of code, the array of objects approach is much more clear about what each property's purpose is. With a two-dimensional array, there is nothing labeling what each index represents. For that reason alone, I would recommend using an array of objects in this case.

answered Apr 16, 2015 at 4:48

nderscore

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