Re-organize a javascript array of objects

Question

I've got an array of question and different answers (which I build dynamically, so the number of entries and different answers can vary):

var qaArray = [
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer C"},
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer C"},
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
]

I need a function to build another array object from this, which would hold the 'answer' and 'count', in this case it would be:

[
    { answer: "Answer A", count: 3 },
    { answer: "Answer B", count: 4 },
    { answer: "Answer C", count: 2 },
]

Is there an easy method to do this, without straight forward loops?

I will recommend you to use lodash here and use groupBy to perform it easily — Koushik Chatterjee
– Koushik Chatterjee, Commented Dec 14, 2017 at 11:10

Faly · Accepted Answer · 2017-12-14 11:07:42Z

3

If ES6 is not a problem, it can be done by:

var qaArray = [
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer C"},
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer C"},
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
];

var result = [...new Set(qaArray.map(q => q.answer))].map(a => ({ answer: a, count: qaArray.filter(e => e.answer === a).length }));

console.log(result);

answered Dec 14, 2017 at 11:07

Faly

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Comments

emil · Accepted Answer · 2017-12-14 11:07:41Z

2

If you are looking for solution without reduce or forEach, here is a verbose way using lodash.

_.countBy will give you close result, but if you want to transform it into array as you want, use mapValues.

_.chain(qaArray)
.countBy('answer')
.mapValues(function(value, key) {
  return { answer: key, count: value }
})
.values()
.value()

answered Dec 14, 2017 at 11:07

emil

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Comments

Vipin Kumar · Accepted Answer · 2017-12-14 11:09:01Z

You can use reduce for this. Concept is to push element to accumulator if it doesn't exist and increment the count if it does.

Please find below solution

var qaArray = [
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer C"},
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
    { question: "Question", answer: "Answer C"},
    { question: "Question", answer: "Answer A"},
    { question: "Question", answer: "Answer B"},
]


result = qaArray.reduce((acc, item) => {
  var exist = acc.find(x => x.answer === item.answer);
  if (exist) {
    exist.count += 1;
  } else {
    acc.push({
      answer: item.answer,
      count: 1
    })
  }
  return acc;
}, []);


console.log(result);

dashton · Accepted Answer · 2017-12-14 11:13:51Z

1

You can use Map to key your answers then reduce over the data to get counts, like so:

var result = Array.from(qaArray.reduce((acc, { answer }) => {
  const current = acc.get(answer) || { answer, count: 0 };
  current.count++;
  return acc.set(answer, current);
}, new Map()).values());

console.log(result);

answered Dec 14, 2017 at 11:13

dashton

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