How to turn an array into another using javascript map?

Question

How can I turn this array:

var users = [
  {
    'date':'jan',
    'visits': 2,
    'drops': 1
  },
  {
    'date':'feb',
    'visits': 3,
    'drops': 2
  }
]

into this array:

var newArray = [
  {
    'name': 'visits',
    'data': [
      2, 3
    ]
  },
  {
    'name': 'drops',
    'data': [
      1, 2
    ]
  }
]

using

newArray = users.map(function(){
  return ...
});

Thanks!

You don't want map for this, as users.length and newArray.length are unrelated. You might want forEach instead, and simply add to two objects from there. — Siguza
– Siguza, Commented Feb 22, 2016 at 17:43

madox2 · Accepted Answer · 2016-02-22 17:47:44Z

1

You can reduce it like this:

var result = users.reduce(function(r, i) {
    r[0].data.push(i.visits);
    r[1].data.push(i.drops);
    return r;
}, [
    { name: 'visits', data: [] },
    { name: 'drops', data: [] }
]);

answered Feb 22, 2016 at 17:47

madox2

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Comments

Nina Scholz · Accepted Answer · 2016-02-22 18:02:16Z

Just a more versatile solution.

var users = [{ 'date': 'jan', 'visits': 2, 'drops': 1 }, { 'date': 'feb', 'visits': 3, 'drops': 2 }],
    result = function (data, names) {
        var r = [];
        data.forEach(function (a) {
            names.forEach(function (b, i) {
                r[i] = r[i] || { name: b, data: [] };
                r[i].data.push(a[b])
            });
        });
        return r;
    }(users, ['visits', 'drops']);

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

Mr. Polywhirl · Accepted Answer · 2016-02-22 19:27:11Z

You can transform your array using a reduction function. This is dynamic.

var users = [{
  'date': 'jan',
  'visits': 2,
  'drops': 1
}, {
  'date': 'feb',
  'visits': 3,
  'drops': 2
}];

function transform(data, blacklist) {
  return Object.keys(data[0]).filter(function(key) {
    return blacklist.indexOf(key) === -1;
  }).map(function(key) {
    return data.reduce(function(obj, record) {
      obj.data.push(record[key]);
      return obj;
    }, {
      name: key,
      data: []
    });
  });
}

function print(obj) {
  document.body.innerHTML = '<pre>' + JSON.stringify(obj, null, 2) + '</pre>';
}

print(transform(users, ['date']));

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