Get random X items from array in javascript

Question

I have the following fiddle using test data, and I am looking through data using $.each

I can loop through no problem, but I want to loop through the data, and then get 3 objects from it at random.

Any tips or tricks would help:

https://jsfiddle.net/inkedraskal/pah44qv6/

$.each(testData,function(x, blah){
    //console.log(blah._id);

  //this gets each objects id & picture, but I want to get 3 random objects, and their corresponding data
  var activeValue = blah._id,
        pictureValue = blah.picture;


  var markUp = '';

  markUp += activeValue + pictureValue;

  console.log(markUp);
});

with the question below, they need to be unique**

Are looking only for a solution that uses $.each? Is there a specific reason for that? You can check my answer, let me know if it OK. — Dekel
– Dekel, Commented Sep 24, 2016 at 2:19

Dekel · Accepted Answer · 2016-09-24 02:17:28Z

The function in the snippet below gets an array and a number (X) of items and returns a new array with X unique random items from the original array:

function getRandomItems(arr, items) {
  var ret = [];
  var indexes = [];
  var arr_length = arr.length;
  
  // If we don't have enough items to return - return the original array
  if (arr_length < items) {
    return arr;
  }
  
  while (ret.length < items) {
    i = Math.floor(Math.random() * arr_length);
    if (indexes.indexOf(i) == -1) {
      indexes[indexes.length] = i;
      ret[ret.length] = arr[i];
    }
  }
  return ret;
}

arr = ['a', 'b', 'c', 'd', 'e']
console.log(getRandomItems(arr, 2))

You can also add the function to the Array.prototype if you want to use it on every Array in your code as a "native" function:

Array.prototype.getRandomItems = function(items) {
  var ret = [];
  var indexes = [];
  var arr_length = this.length;
  
  // If we don't have enough items to return - return the original array
  if (arr_length < items) {
    return this;
  }
  
  while (ret.length < items) {
    i = Math.floor(Math.random() * arr_length);
    if (indexes.indexOf(i) == -1) {
      indexes[indexes.length] = i;
      ret[ret.length] = this[i];
    }
  }
  return ret;
}

arr1 = ['a', 'b', 'c', 'd', 'e']
arr2 = ['aaa', 'bbb', 'ccc', 'ddd', 'eee']

console.log(arr1.getRandomItems(1))
console.log(arr1.getRandomItems(2))
console.log(arr2.getRandomItems(3))
console.log(arr2.getRandomItems(4))

Michał Pietraszko · Accepted Answer · 2016-09-24 01:53:19Z

1

We can create getRandomEntry() function which will return one of the array's elements by using Math.random() function. We'll create a loop which will take random entry every time it iterates.

function getRandomEntry() {
  return testData[Math.round(Math.random() * (testData.length - 1))];
}

for (var i=0; i<3; i++) {
  var entry = getRandomEntry();
  console.log(entry._id, entry.picture);
}

If you need an unique entry every time. You can keep random entries in separate array and check if new one is unqiue.

var randomEntries = [];

function getRandomEntry() {
  return testData[Math.round(Math.random() * (testData.length - 1))];
}

function entryExists(entry) {
  return randomEntries.indexOf(entry) > -1;
}

for (var i=0; i<3; i++) {
  var entry;

  do {

    entry = getRandomEntry();

  } while(entryExists(entry))

  randomEntries.push(entry);
  console.log(entry._id, entry.picture);
}

edited Sep 24, 2016 at 1:53

answered Sep 24, 2016 at 1:26

Michał Pietraszko

6,3093 gold badges24 silver badges27 bronze badges

2 Comments

Wesley Smith Over a year ago

This will fail the they need to be unique requirement

Michał Pietraszko Over a year ago

Edited the answer.

Wesley Smith · Accepted Answer · 2016-09-24 01:43:09Z

You could use a recursive function like the below.

Note that this implementation prevents duplicates in the results

function getRandomObjects(array,selected,needed){
    /*
     *@param array array The array to pull from
     *@param selected array The array of results pulled so far
     *@param needed int The number of results we want
     */
    var length = array.length;
    var num = Math.floor(Math.random() * length) + 1; // get random number in bounds of array
    var exists=false; // make sure we didnt already pick this object
    $.each(selected,function(i,obj){
        if(obj.index==num)exists=true;
    })
    if(exists) getRandomObjects(array,selected,needed); // get a new one if this was a duplicate
    else selected.push(array[num]);
    if(selected.length!=needed) return getRandomObjects(array,selected,needed); // get another object if we need more
    else return selected; // return the final result set
}




var testData = [
  {
    "_id": "57e5d1a90c4206b128cd8654",
    "index": 0,
    "guid": "1f3269fc-0822-4c5a-9c52-8055155b407e",
    "isActive": true,
    "balance": "$3,026.95",
    "picture": "http://placehold.it/32x32"
  },
  {
    "_id": "57e5d1a9a986ccb2f41cf7b9",
    "index": 1,
    "guid": "a6b726b6-6466-4e48-8697-1c6bd7b1c79e",
    "isActive": true,
    "balance": "$2,642.74",
    "picture": "http://placehold.it/32x32"
  },
  {
    "_id": "57e5d1a9f98f8b2f6880de32",
    "index": 2,
    "guid": "e7d736cc-19e0-4bcb-8d0a-4d17442d8cee",
    "isActive": true,
    "balance": "$3,341.64",
    "picture": "http://placehold.it/32x32"
  },
  {
    "_id": "57e5d1a9e40ded5b017e45cd",
    "index": 3,
    "guid": "64230ca8-05c0-4c39-a931-794172475a32",
    "isActive": true,
    "balance": "$2,196.13",
    "picture": "http://placehold.it/32x32"
  },
  {
    "_id": "57e5d1a90cc30be769a06d7c",
    "index": 4,
    "guid": "d6618b78-753a-4ad0-bc14-3687d0b99196",
    "isActive": true,
    "balance": "$1,611.62",
    "picture": "http://placehold.it/32x32"
  },
  {
    "_id": "57e5d1a92481a43f50607415",
    "index": 5,
    "guid": "35ec8186-9494-4f89-ab89-bed7f39872c3",
    "isActive": true,
    "balance": "$3,148.87",
    "picture": "http://placehold.it/32x32"
  },
  {
    "_id": "57e5d1a9164f17c558ba7ce1",
    "index": 6,
    "guid": "244970a0-1ce2-405a-8d69-c7903f9bf5eb",
    "isActive": false,
    "balance": "$3,758.13",
    "picture": "http://placehold.it/32x32"
  },
  {
    "_id": "57e5d1a95afde31c5cf592a8",
    "index": 7,
    "guid": "aa30c82d-dd2b-420c-8b30-7d66cec8d10b",
    "isActive": true,
    "balance": "$1,311.40",
    "picture": "http://placehold.it/32x32"
  }
]


var randomObjects=getRandomObjects(testData,[],3);

console.log(randomObjects);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Rahul Jat · Accepted Answer · 2019-08-27 10:14:39Z

0

You can do this

var items = [1, 2, 3, 4, 5];
var newItems = [];

for(var i = 0; i < 3; i++) {
    var idx = Math.floor(Math.random() * items.length);
    newItems.push(items[idx]);
    items.splice(idx, 1);
}

console.log(newItems);

answered Aug 27, 2019 at 10:14

Rahul Jat

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