Randomize JavaScript Array of Objects Based on Certain Key

Question

I have a JavaScript array similar to this:

arrTest = [
  {qId: 1, text:"test a", order: 1},
  {qID: 2, text:"test b", order: 2},
  {qID: 3, text:"test c", order: 3},
  {qID: 4, text:"test d", order: 4}
];

I would like to randomize just the order key so that all other keys remain the same and the original order of the array stays as is:

arrTest = [
  {qId: 1, text:"test a", order: 3},
  {qID: 2, text:"test b", order: 1},
  {qID: 3, text:"test c", order: 4},
  {qID: 4, text:"test d", order: 2}
];

I have found lots or randomize array discussions and functions, but can't seem to find one that targets a specific key and leaves everything else the same.

Any assistance is appreciated.

Thank you!

You're using an array (which is inherently ordered)... why not order the objects using their index and dump the ordering by key? — chazsolo, Mar 28 '18 at 17:19

score 2 · Accepted Answer · answered Mar 28 '18 at 17:24

2

You could map order and take a random value for assignment back to the property.

var arrTest = [{ qId: 1, text:"test a", order: 1 }, { qID: 2, text:"test b", order: 2 }, { qID: 3, text:"test c", order: 3 }, { qID: 4, text:"test d", order: 4 }],
    random = arrTest.map(({ order }) => order);
    
arrTest.forEach(o => o.order = random.splice(Math.floor(Math.random() * random.length), 1)[0]);

console.log(arrTest);

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answered Mar 28 '18 at 17:24

Nina Scholz

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1

Nice trick using splice! I had virtually the same answer but I was stuck on removing the already assigned from the array. As an aside you can use `0| Math.random() * random.length` instead of `Math.floor`, but that definitely doesn't help readability. – zfrisch Mar 28 '18 at 17:34
I ended up using something very similar to your code above. I liked the .splice() of the random array to ultimately make the order random. Thanks! – Mark Mar 28 '18 at 22:37

Ori Drori · Answer 2 · 2018-03-28T17:42:36.723

Extract the order using Array.map(), shuffle (taken from this answer) the order array, and Array.map() the original array with the new order:

const arrTest = [{"qId":1,"text":"test a","order":1},{"qID":2,"text":"test b","order":2},{"qID":3,"text":"test c","order":3},{"qID":4,"text":"test d","order":4}];

function shuffle(array) {
  for (let i = array.length - 1; i > 0; i--) {
      let j = Math.floor(Math.random() * (i + 1));
      [array[i], array[j]] = [array[j], array[i]];
  }
  
  return array;
}

const result = shuffle(arrTest.map((o) => o.order))
  .map((order, i) => ({
    ...arrTest[i],
    order
  }));
  
console.log(result);

score 0 · Answer 3 · answered Mar 28 '18 at 17:47

For such task I would make a usage of lodash library (https://lodash.com/docs), it has many nice features, personally I attach this lib to every javascript project Im doing. Here is sample solution:

_(arrTest)
   .map(element => element.order)
   .shuffle()
   .each( (order, index) => arrTest[index].order = order);

console.log(arrTest);

Randomize JavaScript Array of Objects Based on Certain Key

3 Answers3