Grouping and then mapping data into an array using lodash

Question

I am looking to group some data and then map (what I believe the best way to do it, could be wrong) into an array I have created the following JSFiddle.

JSFiddle

The JSFiddle shows the desired result plus some of my commented out methods.

My code is below:

var answers = [
  { 'question_id': 1, 'id': 1,  'answer': 'Cat' },
  { 'question_id': 1,   'id': 2,  'answer': 'Dog' },
  { 'question_id': 2, 'id': 3,  'answer': 'Fish' },
  { 'question_id': 2,   'id': 4,  'answer': 'Ant' }
];

var result=_.chain(answers).groupBy("question_id").map(function(v, i) {
  return {
    question_id: i,
 //   id: _.get(_.find(v, 'id'), 'id'),
    answers:[
        {id: 1, answer: 'Cat'},
            {id: 2, answer: 'Dog'},
//  {id: _.map(v, 'id'), answer: _.map(v, 'answer'),}
    ] 
  }
}).value();
document.body.innerHTML = '<pre>' + JSON.stringify(result, null, '  ') + '</pre>';

Gruff Bunny · Accepted Answer · 2017-01-24 17:29:24Z

1

You were nearly there. To get the answers without the 'question_id' you need to map across them and omit the property. This could be done using a function for the map:

answers: _.map(v, function(answer){
    return _.omit(answer, 'question_id');
}

or using the omit function where some of the parameters are already applied and then using that as the function for map:

var omitQuestion = _.partialRight(_.omit, 'question_id');

answers: _.map(v, omitQuestion)

answered Jan 24, 2017 at 17:29

Gruff Bunny

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Alec Fenichel · Accepted Answer · 2017-01-24 16:00:17Z

We iterate over each object in the array, and push it to a object with the question_id as the key. If one does not exist we create it. Then we convert the resulting object into an array.

var answers = [
  { 'question_id': 1, 'id': 1,  'answer': 'Cat' },
  { 'question_id': 1,   'id': 2,  'answer': 'Dog' },
  { 'question_id': 2, 'id': 3,  'answer': 'Fish' },
  { 'question_id': 2,   'id': 4,  'answer': 'Ant' }
];
var result = {};
for (var i = 0; i < answers.length; i++) {
  var question_id = answers[i].question_id;
  if(!result[question_id]) {
    result[question_id] = {question_id: question_id, answers: []};
  }
  result[question_id].answers.push({id: answers[i].id, answer: answers[i].answer})
}
result = Object.keys(result).map(function (key) { return result[key]; });
console.log(result);

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