JavaScript - Shuffling Objects inside an object (randomize) [duplicate]

Question

I need to implement a randomization from JSON result.

The format of the JSON is two objects:

result:

Question(object)

[Object { id="4c6e9a41470b19_96235904",  more...}, 
 Object { id="4c784e6e928868_58699409",  more...}, 
 Object { id="4c6ecd074662c5_02703822",  more...}, 6 more...]

Topic(object)

[Object { id="3jhf3533279827_23424234",  more...}, 
 Object { id="4634663466cvv5_43235236",  more...}, 
 Object { id="47hf3892735298_08476548",  more...}, 2 more...]

I want to randomize the order of the objects inside the question object and the topic objects.

Those are not objects, those are arrays containing objects. — T J
– T J, Commented Nov 19, 2014 at 9:52

Guy · Accepted Answer · 2015-12-09 10:39:35Z

38

You could use a Fisher-Yates-Durstenfeld shuffle:

var shuffledQuestionArray = shuffle(yourQuestionArray);
var shuffledTopicArray = shuffle(yourTopicArray);

// ...

function shuffle(sourceArray) {
    for (var i = 0; i < sourceArray.length - 1; i++) {
        var j = i + Math.floor(Math.random() * (sourceArray.length - i));

        var temp = sourceArray[j];
        sourceArray[j] = sourceArray[i];
        sourceArray[i] = temp;
    }
    return sourceArray;
}

edited Dec 9, 2015 at 10:39

Guy

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answered Sep 15, 2010 at 14:12

LukeH

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Comments

pepkin88 · Accepted Answer · 2010-09-15 15:19:13Z

13

Easiest method (not perfect shuffle, but in some cases may be better):

function randomize(a, b) {
    return Math.random() - 0.5;
}

yourQuestionArray.sort(randomize);
yourTopicArray.sort(randomize);

or

yourQuestionArray.sort(function (a, b) {return Math.random() - 0.5;});
yourTopicArray.sort(function (a, b) {return Math.random() - 0.5;});

( http://jsfiddle.net/dJVHs/ )

edited Sep 15, 2010 at 15:19

answered Sep 15, 2010 at 15:10

pepkin88

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2 Comments

LukeH Over a year ago

For larger arrays this will (probably) be slower than a Fisher-Yates shuffle too. The shuffle will be O(n) whereas using sort will (probably) be O(n log n).

pepkin88 Over a year ago

@LukeH OK, you are right. But this is more beautiful :P

gnarf · Accepted Answer · 2010-09-15 14:00:04Z

7

I found this post on using the Fisher-Yates algorithm to shuffle an array in JavaScript. It uses this function:

function fisherYates ( myArray ) {
  var i = myArray.length;
  if ( i == 0 ) return false;
  while ( --i ) {
     var j = Math.floor( Math.random() * ( i + 1 ) );
     var tempi = myArray[i];
     var tempj = myArray[j];
     myArray[i] = tempj;
     myArray[j] = tempi;
   }
}

answered Sep 15, 2010 at 14:00

gnarf

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1 Comment

pepkin88 Over a year ago

You don't have to make tempj

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