array_rand

(PHP 4, PHP 5)

array_randPick one or more random entries out of an array

Description

mixed array_rand ( array $array [, int $num = 1 ] )

Picks one or more random entries out of an array, and returns the key (or keys) of the random entries.

Parameters

array

The input array.

num

Specifies how many entries should be picked.

Return Values

When picking only one entry, array_rand() returns the key for a random entry. Otherwise, an array of keys for the random entries is returned. This is done so that random keys can be picked from the array as well as random values. Trying to pick more elements than there are in the array will result in an E_WARNING level error, and NULL will be returned.

Changelog

Version Description
5.2.10 The resulting array of keys is no longer shuffled.

Examples

Example #1 array_rand() example

<?php
$input 
= array("Neo""Morpheus""Trinity""Cypher""Tank");
$rand_keys array_rand($input2);
echo 
$input[$rand_keys[0]] . "\n";
echo 
$input[$rand_keys[1]] . "\n";
?>

See Also

add a note add a note

User Contributed Notes 28 notes

up
27
Sebmil
3 years ago
Looks like this function has a strange randomness.

If you take any number of elements in an array which has 40..100 elements, the 31st one is always by far the less occuring (by about 10% less than others).

I tried this piece of code at home (PHP Version 5.3.2-1ubuntu4.9) and on my server (PHP Version 5.2.17), unfortunately i haven't any server with the last version here :

<?php
$valeurs
= range(1, 40);
$proba = array_fill(1, 40, 0);
for (
$i = 0; $i < 10000; ++$i)
{
   
$tirage_tab = array_rand($valeurs, 10);
    foreach(
$tirage_tab as $key => $value)
    {
       
$proba[$valeurs[$value]]++;
    }
}

asort($proba);
echo
"Proba : <br/>\n";
foreach(
$proba as $key => $value)
{
    echo
"$key : $value<br/>\n";
}
?>

In every try, the number of occurrences change a bit but the 31 is always far less (around 2200) than the others (2400-2600). I tried with 50 and 100 elements, no change. I tried with more or less elements to pick (second parameter to array_rand), same result. If you pick only one element it's even worse : 31 has half the result of the others.

For this particular case, i recommend shuffling the array and taking the nth first elements, in this test it's 60% faster and the statistics are ok.
up
12
qeremy
2 years ago
An example for getting random value from arrays;

<?php
function array_random($arr, $num = 1) {
   
shuffle($arr);
   
   
$r = array();
    for (
$i = 0; $i < $num; $i++) {
       
$r[] = $arr[$i];
    }
    return
$num == 1 ? $r[0] : $r;
}

$a = array("apple", "banana", "cherry");
print_r(array_random($a));
print_r(array_random($a, 2));
?>

cherry
Array
(
    [0] => banana
    [1] => apple
)

And example for getting random value from assoc arrays;

<?php
function array_random_assoc($arr, $num = 1) {
   
$keys = array_keys($arr);
   
shuffle($keys);
   
   
$r = array();
    for (
$i = 0; $i < $num; $i++) {
       
$r[$keys[$i]] = $arr[$keys[$i]];
    }
    return
$r;
}

$a = array("a" => "apple", "b" => "banana", "c" => "cherry");
print_r(array_random_assoc($a));
print_r(array_random_assoc($a, 2));
?>

Array
(
    [c] => cherry
)
Array
(
    [a] => apple
    [b] => banana
)
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6
Jordan Doyle
1 year ago
Note: array_rand uses the libc generator, which is slower and less-random than Mersenne Twister.

<?php
    $a
= ['http://php.net/', 'http://google.com/', 'http://bbc.co.uk/'];

   
$website = $a[mt_rand(0, count($a) - 1)];
?>

This is a better alternative.
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2
asarnoNOSPAM@interbaun DOT com
11 years ago
It is correct that using array_rand() with num_req=1 will return an integer and not an array, but why get so complicated with getting just the one value.  The K.I.S.S. method would suggest to do it this way:

<?
srand((double)microtime() * 10000000);
$originalArray = array("red", "blue", "green", "brown",
"cyan", "magenta", "purle", "cheezy");
$pickOne = array_rand($originalArray, 1);
$aRandomSelection = $originalArray[$pickOne ];
echo "$aRandomSelection was the random selection made";
?>

You only need to use the foreach if the num_req >=2. In those cases the array_rand() function will return an array of random elements which are a subset of the original array.  When num_req = 1, the array_rand() function returns an integer that signifies a randomly picked key of the original array.  Hope this clarifies things ... it works for me.
up
3
Anonymous
4 years ago
If the array elements are unique, and are all integers or strings, here is a simple way to pick $n random *values* (not keys) from an array $array:

<?php array_rand(array_flip($array), $n); ?>
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2
nospamplease at mail dot com
1 year ago
Random choice with a closure.

$randomChoice  = function($array) {return $array[array_rand($array)];};

$names = ['Dexter', 'Esther', 'David', 'Richard', 'Rachel', 'Belinda'];

echo $randomChoice($names);
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3
uvm at sun dot he dot net
13 years ago
If you're just trying to draw a random subset of n elements from an array, it seems more effecient to do something like this:

<?php
function draw_rand_array($array,$draws)
{
       
$lastIndex = count($array) - 1;
       
$returnArr = array();
        while(
$draws > 1)
        {
               
$rndIndex = rand(0,$lastIndex);
               
array_push($returnArr,array_splice($array,$rndIndex,1));
               
$draws--;
               
$lastIndex--;
        }

        return
$returnArr;
}
?>

No messing with indexes when you're done... you just have an array with the elements you're looking for in it.
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1
mickoz[at]parodius[dot]com
11 years ago
For those of you thinking that it does not work for num_req = 1, it is because it return a variable and not an array.  This mainly cause some problem with people using foreach.

The correct way to handle this is explained by that example:

<?php
$some_array
= array("blah","bleh","foo","lele");

$nb_value = 1;

srand ((float) microtime() * 10000000);
$rand_keys = array_rand($some_array, $nb_value);

if(!
is_array($rand_keys))
{
 
$rand_keys = array($rand_keys);
}

print_r($rand_keys); // verify here the array of keys
echo "\n<BR>";
?>

// You can then correctly use the foreach, as it require an array to work
// If you use foreach with one element, it won't work.

<?php
$random_array
= array();

foreach(
$rand_keys as $value)
{
 
array_push($random_array, $some_array[$value]);
}

print_r($random_array);
?>
up
1
josh at 3io dot com
12 years ago
I modified fake_array_rand to always only return 1 element, and did some benchmarks against calling array_rand with the second parameter as 1.  I ran 100 samples for each function for each number of elements and took the average result.  While the internal array_rand is faster for a small number of elements, it scales very poorly.

1 elements: 2.0619630813599E-05 sec. for array_rand,8.4352493286133E-05 sec. for fake_array_rand
10 elements: 2.1675825119019E-05 sec. for array_rand,8.427619934082E-05 sec. for fake_array_rand
100 elements: 2.9319524765015E-05 sec. for array_rand,8.4599256515503E-05 sec. for fake_array_rand
1000 elements: 0.0001157283782959 sec. for array_rand,8.5572004318237E-05 sec. for fake_array_rand
10000 elements: 0.0016669762134552 sec. for array_rand,8.5201263427734E-05 sec. for fake_array_rand
100000 elements: 0.015599734783173 sec. for array_rand,8.5580348968506E-05 sec. for fake_array_rand
1000000 elements: 0.18011983394623 sec. for array_rand,8.6690187454224E-05 sec. for fake_array_rand

<?php
function fake_array_rand ($array)
{
       
$count = count ($array);
       
# Help keep the number generator random :)
       
$randval and usleep ("0.$randval");

       
# Seed the random number generator
        # Generate a random number
       
srand ((double) microtime() * 10000000);
       
$randval = rand();

       
# Use the random value to 'pick' an entry from the array
        # Count the number of times that the entry is picked
       
++$index[$randval % $count];

        return
$array[$randval % $count];
}
?>
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3
herodesh [-at_] gmail [-dot-] com
7 years ago
this is to generate a random selection from an array with array_rand preety nice, can be used to generate random passwords or anything:

$my_array = array("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "0", "1", "2", "3", "4", "5");
        for ($i=0; $i<=10; $i++)
        {
            $random = array_rand($my_array);
                        //this generates the random number from the array
            $parola .= $my_array[$random];
                        //here we will display the exact charachter from the array
        }
        echo $parola; // printing result
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2
dragonfly at dragonflyeye dot net
8 years ago
Well, this is interesting.   I don't see anyone else commenting on this, so just in case you were planning to use this function like I was, be prepared: array_rand does not handle multidimensional arrays.  It just ends up returning a list of the X-axis values without the Y-axis arrays.  Bummer.  I'm going to have to find another way to do what I wanted.
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1
Will-ster
8 years ago
This is something I have been playing with for quite awhile. I'm very new to php, but i finally got it to work. it's a function that will take and array[$arrquo] and find a particular keyword[$find] in the different elements of the array then take those elements that posess that keyword and display them at random

<?php
function popbyword($arrquo,$find)
{
$newarr = array('');
foreach(
$arrquo as $line)
{
  if(
strstr( $line, $find ) )
  {
   
array_push($newarr, $line);

  }
}   
srand((double)microtime()*1000000);
$rquote = array_rand($newarr);
echo
$newarr[$rquote];
}

popbyword($images, 'Albert');
?>

In my case I had this huge array of quotes with 90 some elements. I was able to find certain keywords in those elements then ONLY display the elements that had those keywords. NEAT! Maybe only because I'm new.
up
2
jpinedo
10 years ago
An array of arrays example:

<?php
$banners
[0]['imagen']="imagen0.gif";
$banners[0]['url']="www.nosenada.tal";

$banners[1]['imagen']="imagen1.gif";
$banners[1]['url']="www.nose.tal";

$banners[2]['imagen']="imagen2.gif";
$banners[2]['url']="pagina.html";

$banners[3]['imagen']="imagen3.jpg";
$banners[3]['url']="../pagina.php";

$id_banner = array_rand($banners);

echo 
"Archivo:--".$banners[$id_banner]['imagen']. "<br />\n";
echo 
"URL:-----".$banners[$id_banner]['url']. "<br />\n";
?>
up
1
admin at jeremyzaretski dot com
5 years ago
<?php
// a foreach friendly version of array_rand
function Select_Random_Indices($source_array, $count = 1)
{
    if(
$count > 0)
    {
        if(
$count == 1)
        {
           
$result = array(array_rand($source_array, $count));
        }
        else
        {
           
$result = array_rand($source_array, $count);
        }
    }
    else
    {
       
$result = array();
    }

    return
$result;
}

// using the above function to pick random values instead of entries
function Select_Random_Entries($source_array, $count = 1)
{
   
$result = array();
   
$index_array = Select_Random_Indices($source_array, $count);

    foreach(
$index_array as $index)
    {
       
$result[$index] = $source_array[$index];
    }

    return
$result;
}
?>
up
1
maxnamara at yahoo dot com
9 years ago
<?php
$input
= array("Neo", "Morpheus", "Trinity", "Cypher", "Tank");

function
my_array_rand($input,$i=2){
srand((float) microtime() * 10000000);

$rand_keys = array_rand($input, $i);

/*
print $input[$rand_keys[0]] . "\n";
print $input[$rand_keys[1]] . "\n";
*/

$res = array();

if(
$i > 1){

for(
$a=0;$a<$i;$a++){

   
$res[] = $input[$rand_keys[$a]];
   
}

}
else{

   
$res[] = $input[$rand_keys];   
   
}

return
$res;
}

$a = my_array_rand($input,3);
echo
"<pre>";
print_r($a);
echo
"</pre>";
?>
up
1
Paul Hodel (paul at ue dot com dot br)
11 years ago
If you trying to get a randon array just use that... it's easier! And you have no repeats...

<?

srand ((float) microtime() * 10000000);

$input = array ("Neo", "Morpheus", "Trinity", "Cypher", "Tank");

$keys = array_rand ($input, sizeof($input));

while (list($k, $v) = each($keys))
{
    echo $new_input = $input[$v];
}

?>
up
1
info at pavliga dot com
5 years ago
If you want get unique range:

<?php
$n
= 15;

$data = range(1, 20);
$rand = array_rand($data,$n);

for(
$i=0; $i<$n; $i++)
{
echo
$rand[$i]."<br>";
}

?>
up
1
Frederick Lemasson aka djassper at gmail
7 years ago
To select a random Value (not a Key) from a Multi-Dimentionnal array I made a recursive function : array_multi_rand()

the following exemple randomly selects an url from a multidimentionnal array :

<?

$Expos['Google']['Science']='news.google.fr/news?topic=t';
$Expos['Google']['Economie']='news.google.fr/news?topic=b';
$Expos['Google']['Sante']='news.google.fr/news?topic=m';
$Expos['Yahoo']='fr.news.yahoo.com';
$Expos['Events']['LogicielLibre']='agendadulibre.org';
$Expos['MyBlog']='www.kik-it.com';

function array_multi_rand($Zoo){
    $Boo=array_rand($Zoo);
    if(is_array($Zoo[$Boo])){
        return array_multi_rand($Zoo[$Boo]);
    }else{
        return $Zoo[$Boo];
    }
}

echo(array_multi_rand($Expos));

?>
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1
alexkropivko at(dog) yandex dot ru
9 years ago
There was a mistake at "Paul Hodel (paul at ue dot com dot br) 17-Apr-2003 04:40":
String
echo $new_input = $input[$v];

have to be:
echo $new_input[] = $input[$v];
up
1
scandar at home dot se
11 years ago
Note that the int num_req parameter is the required number of element to randomly select. So if your array has 3 element and num_req=4 then array_rand() will not return anything since it is impossible to select 4 random elements out of an array that only contains 3 elements. Many people think that they will get 3 elements returned but that is of course not the case.
up
1
john at brahy dot com
4 months ago
if you want random elements from an array, this worked pretty well for me.

<?php
//using shuffle randomizes the order of elements

function get_random_elements( $array,$limit = 0 ) {
   
   
shuffle($array);

    if (
$limit > 0 ) {
       
$array = array_splice($array, 0, $limit);
    }
    return
$array;
}
?>
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0
BenedictLemieux at gmail dot com
4 days ago
Two things always bugged me with array_rand().

First is its name. It does not sound clear enough whether it gives key or values.

Second and more importantly is its erratic randomness, which is already well documented.

That is why I came up with these two simple functions:

<?php
function random_key($array){
   
$keys=array_keys($array);
    return
$keys[mt_rand(0, count($keys) - 1)];
}   
function
random_value($array){
   
$values=array_values($array);
    return
$values[mt_rand(0, count($values) - 1)];
}
?>

They both work well with any kind of arrays, do not alter the original one like shuffle, are giving more realistic random results, and their names are self describing.

The main drawback is that, as opposed to array_rand, they only gives one element, but at least that is clear from their name. I do believe easy to make random_keys and random_values.
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0
marco at behnke dot biz
6 days ago
Is there a difference in randomness if you use shuffle instead?

<?php
function array_shuffle($input, $num_of_results) {
   
shuffle($input);
    return
array_chunk($input, $num_of_results, true)[0];
}

$input = array("Neo", "Morpheus", "Trinity", "Cypher", "Tank");
var_dump(array_shuffle($input, 2));

/*
array(2) {
  [0]=>
  string(3) "Neo"
  [1]=>
  string(8) "Morpheus"
}
*/
?>

And yes, I know that my example returns a portion of the array and not just the key numbers
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0
JS
8 years ago
I wanted to write something that picks a random entry from a 1column-MySQL database - simply Post Of The Moment (potm). I know there surly are many better ways to do it, but I`m rather new to PHP :)  Anyway, it`s simple and no-problem working code.
Of course I assume your DB exists and you always have something in it.

@$link = MySQL_Connect("localhost", "username", "password"); //connect to mysql
mySQL_Select_DB("database"); //..to DB
@$potms = MySQL_Query("SELECT * FROM potm"); //now we get all from our table and store it
MySQL_Close($link); //there`s no need for connection, so we should close it

$potm_array = ''; //sets variables to "zero" values
$i = 0;
while ($entry = MySQL_Fetch_Array($potms)) //now we go through our DB
       {
         $potm_array[$i] = $entry; //our temporary array from which we will random pick a field key
         $i++; //now we increment our field key
       }

$potm_id = array_rand($potw_array); //picks a random key from array
$potm = $potm_array[$potm_id]['name_of_the_field']; //now we have stored our Post Of The Moment in $potm

..hope this helps
up
0
trukin at gmail dot com
8 years ago
Modify of last note:
<?php
if (!function_exists('array_rand')) {
    function
array_rand($array, $lim=1) {
       
mt_srand((double) microtime() * 1000000);
        for(
$a=0; $a<=$lim; $a++){
           
$num[] = mt_srand(0, count($array)-1);
        }
        return @
$num;
    }
}
?>

mt_rand generates a better random number, and with the limit.
up
0
bjcffnet at gmail dot com
9 years ago
As wazaawazaa600 at msn dot com pointed out, a multi-dimensional array doesn't work with this function. So, I hope I can help someone with this :)

<?php
/**
* Returns a number of random elements from an array.
*
* It returns the number (specified in $limit) of elements from
* $array. The elements are returned in a random order, exactly
* as it was passed to the function. (So, it's safe for multi-
* dimensional arrays, aswell as array's where you need to keep
* the keys)
*
* @author Brendan Caffrey  <bjcffnet at gmail dot com>
* @param  array  $array  The array to return the elements from
* @param  int    $limit  The number of elements to return from
*                            the array
* @return array  The randomized array
*/
function array_rand_keys($array, $limit = 1) {
   
$count = @count($array)-1;

   
// Sanity checks
   
if ($limit == 0 || !is_array($array) || $limit > $count) return array();
    if (
$count == 1) return $array;

   
// Loop through and get the random numbers
   
for ($x = 0; $x < $limit; $x++) {
       
$rand = rand(0, $count);

       
// Can't have double randoms, right?
       
while (isset($rands[$rand])) $rand = rand(0, $count);

       
$rands[$rand] = $rand;
    }

   
$return = array();
   
$curr = current($rands);

   
// I think it's better to return the elements in a random
    // order, which is why I'm not just using a foreach loop to
    // loop through the random numbers
   
while (count($return) != $limit) {
       
$cur = 0;

        foreach (
$array as $key => $val) {
            if (
$cur == $curr) {
               
$return[$key] = $val;

               
// Next...
               
$curr = next($rands);
                continue
2;
            } else {
               
$cur++;
            }
        }
    }

    return
$return;
}
?>
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0
yhoko at yhoko dot com
10 years ago
According to office at at universalmetropolis dot com I have to say that the example is wrong.

<?php
// retrieve one of the options at random from the array
$teamcolours = $teamcolours[rand(0,count($teamcolours))];
?>

The count() function will return the number of items in the array, that's the last index + 1. So if there's 2 items in the array, count() will return 2 but the indices are 0 and 1. Now since rand(x,y) randomizes between x and y inclusively the index from the above example may be out of bounds. Thus you have to subtract 1 from the count:

<?php
   
// Get random item
   
$teamcolours = $teamcolours[rand(0,count($teamcolours)-1)];
?>
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-1
Anonymous
2 years ago
It doesn't explicitly say it in the documentation, but PHP won't pick the same key twice in one call.
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