Как найти рандом в массиве

It’s a simple one-liner:

const randomElement = array[Math.floor(Math.random() * array.length)];

For example:

const months = ["January", "February", "March", "April", "May", "June", "July"];

const random = Math.floor(Math.random() * months.length);
console.log(random, months[random]);

If you’ve already got underscore or lodash included in your project you can use _.sample.

// will return one item randomly from the array
_.sample(['January', 'February', 'March']);

If you need to get more than one item randomly, you can pass that as a second argument in underscore:

// will return two items randomly from the array using underscore
_.sample(['January', 'February', 'March'], 2);

or use the _.sampleSize method in lodash:

// will return two items randomly from the array using lodash
_.sampleSize(['January', 'February', 'March'], 2);

answered Jun 19, 2015 at 18:40

You may consider defining a function on the Array prototype, in order to create a method [].sample() which returns a random element.

First, to define the prototype function, place this snippet in your code:

Array.prototype.sample = function(){
  return this[Math.floor(Math.random()*this.length)];
}

Later, to sample a random element from the array, just call .sample():

[1,2,3,4].sample() //=> a random element

_{I’m releasing these code snippets into the public domain, under the terms of the CC0 1.0 license.}

answered Nov 24, 2015 at 23:52

~~ is much faster than Math.Floor(), so when it comes to performance optimization while producing output using UI elements, ~~ wins the game. MORE INFO

var rand = myArray[~~(Math.random() * myArray.length)];

But if you know that the array is going to have millions of elements then you might want to reconsider between Bitwise Operator and Math.Floor(), as bitwise operators behave weirdly with large numbers. See below example explained with the output.

var number = Math.floor(14444323231.2); // => 14444323231
var number = 14444323231.2 | 0; // => 1559421343

answered May 5, 2018 at 12:25

The shortest version:

var myArray = ['January', 'February', 'March']; 
var rand = myArray[(Math.random() * myArray.length) | 0]
console.log(rand)

Say you want to choose a random item that is different from the last time (not really random, but still a common requirement)…

/**
 * Return a random element from an array that is
 * different than `last` (as long as the array has > 1 items). 
 * Return null if the array is empty.
*/
function getRandomDifferent(arr, last = undefined) {
  if (arr.length === 0) {
    return null;
  } else if (arr.length === 1) {
    return arr[0];
  } else {
    let num = 0;
    do {
      num = Math.floor(Math.random() * arr.length);
    } while (arr[num] === last);
    return arr[num];
  }
}

Implement like this:

const arr = [1,2,3];
const r1 = getRandomDifferent(arr);
const r2 = getRandomDifferent(arr, r1); // r2 is different than r1.

answered Aug 14, 2012 at 1:57

If you have fixed values (like a month name list) and want a one-line solution

var result = ['January', 'February', 'March'][Math.floor(Math.random() * 3)]

The second part of the array is an access operation as described in Why does [5,6,8,7][1,2] = 8 in JavaScript?

If you want to write it on one line, like Pascual’s solution, another solution would be to write it using ES6’s find function (based on the fact, that the probability of randomly selecting one out of n items is 1/n):

var item = ['A', 'B', 'C', 'D'].find((_, i, ar) => Math.random() < 1 / (ar.length - i));
console.log(item);

Use that approach for testing purposes and if there is a good reason to not save the array in a seperate variable only. Otherwise the other answers (floor(random()*length and using a seperate function) are your way to go.

answered Sep 11, 2017 at 18:01

answered Aug 5, 2022 at 5:26

SeagullSeagull

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ManngoManngo

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Faker.js has many utility functions for generating random test data. It is a good option in the context of a test suite:

const faker = require('faker');
faker.helpers.arrayElement(['January', 'February', 'March']);

As commenters have mentioned, you generally should not use this library in production code.

let rndItem = a=> a[rnd()*a.length|0];
let rnd = ()=> crypto.getRandomValues(new Uint32Array(1))[0]/2**32;

var myArray = ['January', 'February', 'March'];

console.log( rndItem(myArray) )

Kamil KiełczewskiKamil Kiełczewski

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dwiltdwilt

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Max HeiberMax Heiber

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var myArray = ['January', 'February', 'March'];    
var item = myArray[(Math.random()*myArray.length)|0];
console.log('item:', item);

Pavel PPavel P

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Simple Function :

var myArray = ['January', 'February', 'March'];
function random(array) {
     return array[Math.floor(Math.random() * array.length)]
}
random(myArray);

OR

var myArray = ['January', 'February', 'March'];
function random() {
     return myArray[Math.floor(Math.random() * myArray.length)]
}
random();

OR

var myArray = ['January', 'February', 'March'];
function random() {
     return myArray[Math.floor(Math.random() * myArray.length)]
}
random();

answered Dec 17, 2017 at 5:42

In my opinion, better than messing around with prototypes , or declaring it just in time, I prefer exposing it to window:

window.choice = function() {
  if (!this.length || this.length == 0) return;
  if (this.length == 1) return this[0];
  return this[Math.floor(Math.random()*this.length)];
}

Now anywhere on your app you call it like:

var rand = window.choice.call(array)

This way you can still use for(x in array) loop properly

answered May 13, 2014 at 10:27

I’ve found a way around the top answer’s complications, just by concatenating the variable rand to another variable that allows that number to be displayed inside the calling of myArray[];. By deleting the new array created and toying around with it’s complications, I’ve come up with a working solution:

<!DOCTYPE html>
<html>
<body>

<p id="demo"></p>

<script>

var myArray = ['January', 'February', 'March', 'April', 'May'];    

var rand = Math.floor(Math.random() * myArray.length);

var concat = myArray[rand];

function random() {
   document.getElementById("demo").innerHTML = (concat);
}
</script>

<button onClick="random();">
Working Random Array generator
</button>

</body>
</html>

answered Apr 27, 2016 at 22:01

static generateMonth() { 
const theDate = ['January', 'February', 'March']; 
const randomNumber = Math.floor(Math.random()*3);
return theDate[randomNumber];
};

Neil MeyerNeil Meyer

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blagusblagus

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Array.prototype.random = function(n){
  if(n&&n>1){
    const a = [];
    for(let i = 0;i<n;i++){
      a.push(this[Math.floor(Math.random()*this.length)]);
    }
    return a;
  } else {
    return this[Math.floor(Math.random()*this.length)];
  }
}

const mySampleArray =  ['a','b','c','d','e','f','g','h'];

mySampleArray.random(); // return any random value etc. 'a', 'b'
mySampleArray.random(3); //retun an array with random values etc: ['b','f','a'] , ['d','b','d']

alert(mySampleArray.random());
alert(mySampleArray.random(3));

Kamuran SönecekKamuran Sönecek

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let some_array = ['Jan', 'Feb', 'Mar', 'Apr', 'May'];
let months = random_elems(some_array, 3);

console.log(months);

function random_elems(arr, count) {
  let len = arr.length;
  let lookup = {};
  let tmp = [];

  if (count > len)
    count = len;

  for (let i = 0; i < count; i++) {
    let index;
    do {
      index = ~~(Math.random() * len);
    } while (index in lookup);
    lookup[index] = null;
    tmp.push(arr[index]);
  }

  return tmp;
}

RafaelRafael

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Here is an example of how to do it:

$scope.ctx.skills = data.result.skills;
    $scope.praiseTextArray = [
    "Hooray",
    "You're ready to move to a new skill", 
    "Yahoo! You completed a problem", 
    "You're doing great",  
    "You succeeded", 
    "That was a brave effort trying new problems", 
    "Your brain was working hard",
    "All your hard work is paying off",
    "Very nice job!, Let's see what you can do next",
    "Well done",
    "That was excellent work",
    "Awesome job",
    "You must feel good about doing such a great job",
    "Right on",
    "Great thinking",
    "Wonderful work",
    "You were right on top of that one",
    "Beautiful job",
    "Way to go",
    "Sensational effort"
  ];

  $scope.praiseTextWord = $scope.praiseTextArray[Math.floor(Math.random()*$scope.praiseTextArray.length)];

Create one random value and pass to array

Please try following code..

//For Search textbox random value
var myPlaceHolderArray = ['Hotels in New York...', 'Hotels in San Francisco...', 'Hotels Near Disney World...', 'Hotels in Atlanta...'];
var rand = Math.floor(Math.random() * myPlaceHolderArray.length);
var Placeholdervalue = myPlaceHolderArray[rand];

alert(Placeholdervalue);

answered Feb 3, 2017 at 12:49

randojs makes this a little more simple and readable:

console.log( rando(['January', 'February', 'March']).value );

<script src="https://randojs.com/1.0.0.js"></script>

answered Dec 2, 2019 at 2:47

I am really surprised nobody tried to use native random values:

array[Date.now()%array.length]

It will not work for array length over 160000000000, but I am sure you will never create arrays like this

UPD

As far as you question is how to pick random value from array called myArray (with len=3), the solution should be:

myArray[Date.now()%myArray.length]

answered Nov 3, 2021 at 5:38

I have an array called $ran = array(1,2,3,4);

I need to get a random value out of this array and store it in a variable, how can I do this?

$value = $array[array_rand($array)];

answered Jan 12, 2015 at 14:18

You could use the array_rand function to select a random key from your array like below.

$array = array("one", "two", "three", "four", "five", "six");
echo $array[array_rand($array, 1)];

or you could use the rand and count functions to select a random index.

$array = array("one", "two", "three", "four", "five", "six");
echo $array[rand(0, count($array) - 1)];

answered Oct 7, 2013 at 22:38

Derived from Laravel Collection::random():

function array_random($array, $amount = 1)
{
    $keys = array_rand($array, $amount);

    if ($amount == 1) {
        return $array[$keys];
    }

    $results = [];
    foreach ($keys as $key) {
        $results[] = $array[$key];
    }

    return $results;
}

Usage:

$items = ['foo', 'bar', 'baz', 'lorem'=>'ipsum'];

array_random($items); // 'bar'
array_random($items, 2); // ['foo', 'ipsum']

A few notes:

• $amount has to be less than or equal to count($array).
• array_rand() doesn’t shuffle keys (since PHP 5.2.10, see 48224), so your picked items will always be in original order. Use shuffle() afterwards if needed.

Documentation: array_rand(), shuffle()

edit: The Laravel function has noticeably grown since then, see Laravel 5.4’s Arr::random(). Here is something more elaborate, derived from the grown-up Laravel function:

function array_random($array, $number = null)
{
    $requested = ($number === null) ? 1 : $number;
    $count = count($array);

    if ($requested > $count) {
        throw new RangeException(
            "You requested {$requested} items, but there are only {$count} items available."
        );
    }

    if ($number === null) {
        return $array[array_rand($array)];
    }

    if ((int) $number === 0) {
        return [];
    }

    $keys = (array) array_rand($array, $number);

    $results = [];
    foreach ($keys as $key) {
        $results[] = $array[$key];
    }

    return $results;
}

A few highlights:

• Throw exception if there are not enough items available
• array_random($array, 1) returns an array of one item (#19826)
• Support value “0” for the number of items (#20439)

answered Oct 15, 2015 at 11:32

In my case, I have to get 2 values what are objects. I share this simple solution.

$ran = array("a","b","c","d");
$ranval = array_map(function($i) use($ran){return $ran[$i];},array_rand($ran,2));

answered Jun 23, 2019 at 9:37

This will work nicely with in-line arrays. Plus, I think things are tidier and more reusable when wrapped up in a function.

function array_rand_value($a) {
    return $a[array_rand($a)];
}

Usage:

array_rand_value(array("a", "b", "c", "d"));

On PHP < 7.1.0, array_rand() uses rand(), so you wouldn’t want to this function for anything related to security or cryptography. On PHP 7.1.0+, use this function without concern since rand() has been aliased to mt_rand().

answered May 2, 2019 at 23:20

I needed one line version for short array:

($array = [1, 2, 3, 4])[mt_rand(0, count($array) - 1)]

or if array is fixed:

[1, 2, 3, 4][mt_rand(0, 3]

answered Oct 21, 2019 at 2:56

Does your selection have any security implications? If so, use random_int() and array_keys(). (random_bytes() is PHP 7 only, but there is a polyfill for PHP 5).

function random_index(array $source)
{
    $max = count($source) - 1;
    $r = random_int(0, $max);
    $k = array_keys($source);
    return $k[$r];
}

Usage:

$array = [
    'apple' =>   1234,
    'boy'   =>   2345,
    'cat'   =>   3456,
    'dog'   =>   4567,
    'echo'  =>   5678,
    'fortune' => 6789
];
$i = random_index($array);
var_dump([$i, $array[$i]]);

Demo: https://3v4l.org/1joB1

answered Dec 8, 2015 at 6:44

Use rand() to get random number to echo random key. In ex: 0 – 3

$ran = array(1,2,3,4);
echo $ran[rand(0,3)];

answered May 6, 2017 at 15:57

I’m basing my answer off of @ÓlafurWaage’s function. I tried to use it but was running into reference issues when I had tried to modify the return object. I updated his function to pass and return by reference. The new function is:

function &random_value(&$array, $default=null)
{
    $k = mt_rand(0, count($array) - 1);
    if (isset($array[$k])) {
        return $array[$k];
    } else {
        return $default;
    }
}

For more context, see my question over at Passing/Returning references to object + changing object is not working

Get random values from an array.

function random($array)
{
    /// Determine array is associative or not
    $keys = array_keys($array);
    $givenArrIsAssoc = array_keys($keys) !== $keys;

    /// if array is not associative then return random element
    if(!$givenArrIsAssoc){
        return $array[array_rand($array)];
    }

    /// If array is associative then 
    $keys = array_rand($array, $number);
    $results = [];
    foreach ((array) $keys as $key) {
        $results[] = $array[$key];
    }
    return $results;
}

answered Sep 7, 2020 at 16:36

mt_srand usage example

if one needs to pick a random row from a text but same all the time based on something

$rows = array_map('trim', explode("n", $text));
mt_srand($item_id);
$row = $rows[rand(0, count($rows ) - 1)];

answered Sep 23, 2022 at 19:21

A simple way to getting Randdom value form Array.

$color_array =["red","green","blue","light_orange"];
$color_array[rand(0,3)

now every time you will get different colors from Array.

answered Apr 12, 2020 at 20:50