Transform Array of objects into 2D array

Question

I want transform an array of objects into 2D array (array of arrays). I try with map and Object.keys(), but I want push the first value of each objects into the first array, the second value of each objects into the second array, etc ... Thank you for your answers.

The good result

[
  ['2', '5', '8', '10', '12'],
  ['4', '10', '16', '20', '24'],
  ['6', '15', '24', '30', '36'],
  ['10', '25', '40', '50', '60']
]

The actual result

[
  ['2', '4', '6', '10'],
  ['5', '10', '15', '25'],
  ['8', '16', '24', '40'],
  ['10', '20', '30', '50'],
  ['12', '24', '36', '60']
]

let obj = [
  {
    line1: '2',
    line2: '4',
    line3: '6',
    line4: '10'
  }, {
    line1: '5',
    line2: '10',
    line3: '15',
    line4: '25'
  }, {
    line1: '8',
    line2: '16',
    line3: '24',
    line4: '40'
  }, {
    line1: '10',
    line2: '20',
    line3: '30',
    line4: '50'
  }, {
    line1: '12',
    line2: '24',
    line3: '36',
    line4: '60'
  }
];

var output = obj.map(function(obj) {
  return Object.keys(obj).map(function(key) { 
    return obj[key];
  });
});

console.log(output);

**JS Objects are unordered structures** - you can't have a strict order of key/values. https://stackoverflow.com/questions/5525795/does-javascript-guarantee-object-property-order — RomanPerekhrest, Nov 29 '17 at 12:03

score 3 · Accepted Answer · answered Nov 29 '17 at 12:03

You need the indices for transfoming and take the reversed indices for accessing the result set.

var array = [{ line1: '2', line2: '4', line3: '6', line4: '10' }, { line1: '5', line2: '10', line3: '15', line4: '25' }, { line1: '8', line2: '16', line3: '24', line4: '40' }, { line1: '10', line2: '20', line3: '30', line4: '50' }, { line1: '12', line2: '24', line3: '36', line4: '60' }],
    result = array.reduce((r, o, i) => {
        Object.keys(o).forEach((k, j) => (r[j] = r[j] || [])[i] = o[k]);
        return r;
    }, []);

console.log(result);

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For a stable result, you could take the keys as array in advance.

var array = [{ line1: '2', line2: '4', line3: '6', line4: '10' }, { line1: '5', line2: '10', line3: '15', line4: '25' }, { line1: '8', line2: '16', line3: '24', line4: '40' }, { line1: '10', line2: '20', line3: '30', line4: '50' }, { line1: '12', line2: '24', line3: '36', line4: '60' }],
    keys = ['line1', 'line2', 'line3', 'line4'],
    result = array.reduce((r, o, i) => {
        keys.forEach((k, j) => (r[j] = r[j] || [])[i] = o[k]);
        return r;
    }, []);

console.log(result);

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score 1 · Answer 2 · answered Nov 29 '17 at 12:24

You can also use following approach.

let obj = [
  {
    line1: '2',
    line2: '4',
    line3: '6',
    line4: '10'
  }, {
    line1: '5',
    line2: '10',
    line3: '15',
    line4: '25'
  }, {
    line1: '8',
    line2: '16',
    line3: '24',
    line4: '40'
  }, {
    line1: '10',
    line2: '20',
    line3: '30',
    line4: '50'
  }, {
    line1: '12',
    line2: '24',
    line3: '36',
    line4: '60'
  }
];

var output = [];
for(var i = 0; i < obj.length; i++){
   var index = 0;
   for(var values in obj[i]){
      if(output[index] == undefined){
        output[index] = [];
      }
      output[index].push(obj[i][values]);
      index++;
   }
}

console.log(output);

Transform Array of objects into 2D array

2 Answers2