array_rand

add a note User Contributed Notes

dbrooks at icarusstudios dot com
06-Sep-2006 05:28


Instead of looping through all the rows selected to pick a random one, let the server do the work for you:



select * from some_table order by rand() limit 1;

JS
04-Sep-2006 06:07


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

mark at rugbyweb dot org
30-Aug-2006 04:29


I was setting up a rotating add banner and was trying to find a way to go about it using an auto_increment id from the database, so I wrote this little script:



<?php

require "mysql.php";

global $c;

print "<center>";

$qq=mysql_query("SELECT adID FROM ads WHERE adCLICKS<=adMAX",$c) or die (mysql_error()."<br>Error, please report this error quoting #QAB");

while($q=mysql_fetch_array($qq))

{

$ad1[$q['adID']]++; //Used an array and inserted the database query results into it.

}

$ad=array_rand($ad1, 1); //Did a random array function and then used it in the query below.

$er=mysql_query("SELECT * FROM ads WHERE adID='$ad'") or die (mysql_error()."<br>Error, please report this error quoting #QAB3");

if(!mysql_num_rows($er))

{

print "<A href='advertise.php'>Place an ad here!</a>";

exit;

}

$r=mysql_fetch_array($er);

print "<a href='adsout.php?ID={$r['adID']}&BLOCK=1'><img src='{$r['adAD']}' alt='{$r['adNAME']}' height='60' width='468'></a>";

?>

dragonfly at dragonflyeye dot net
08-Jul-2006 04:28


Well, I came up with a workaround for my earlier problem.  For those of you who might need to shuffle around multi-dimensional arrays (I used this to randomize a list of headlines from a MySQL database query), here's what I did to get the desired output:



$subs = //my query went here

$shfl = array_rand($subs, 5);

$shsubs = array();

for ($x=0; $x<count($shfl); $x++) {

    $shsubs[] = $subs[$shfl[$x]];

}



There may in fact be a much easier way to do this, but this is what I came up with and its working!



Thanks to everyone that makes php.net the invaluable tool for us nooobies!

dragonfly at dragonflyeye dot net
07-Jul-2006 10:57


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.

steve at webcommons dot biz
06-Jul-2006 05:12


Following are functions for getting a random key or value (or array of random keys or values) from a filtered array.  In other words, given an array of data, these functions filter out what you don't want, then extract a random element or bunch from what's left.



$CallBack is the filtering function.  



  // Utility function for functions below

  function GetRandomArrayValue($TheArray) {

      return $TheArray[array_rand($TheArray)];

  }

  

  

  // Get a random key or array of keys from a filtered array

  function GetRandomFilteredArrayKeys($aInput, $CallBack = NULL, $NumReq = 1) {

      $FilteredKeys = array_keys(array_filter($aInput, $CallBack));

      

      if ($NumReq <= 1) {

        return GetRandomArrayValue($FilteredKeys);

      }

      else {

        shuffle($FilteredKeys);

        

        return array_slice($FilteredKeys, 0, $NumReq);

      }

  }

  

  // Get a random value or array of values from a filtered array

  function GetRandomFilteredArrayValues($aInput, $CallBack = NULL, $NumReq = 1) {

      $aFiltered = array_filter($aInput, $CallBack);

      

      if ($NumReq <= 1) {      

        return $aFiltered[GetRandomArrayValue(array_keys($aFiltered))];

      }

      else {

        shuffle($aFiltered);

        

        return array_slice($aFiltered, 0, $NumReq);

      }

  }

trukin at gmail dot com
17-Mar-2006 05:23


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.

emailfire at gmail dot com
13-Mar-2006 05:32


<?php

if (!function_exists('array_rand')) {

function array_rand($array) {

srand((double) microtime() * 1000000);

return rand(0, count($array)-1);

}

}

?>

Will-ster
02-Jan-2006 08:18


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.

farooqym at ieee dot org
01-Jan-2006 06:05


Here's an algorithm to make a weighted selection of an item from an array. 

Say we have an array $items with keys as items and values as corresponding weights.

For example:

<?php

$items = array(

    item1 => 3,

    item2 => 4,

    item3 => 5,

);

?>

i.e. we want to choose item1 25% of the time, item2 33.3% of the time and item3 41.6% of the time.

Here's a function that works when the weights are positive integers:

<?php

function array_rand_weighted($values) {

    $r = mt_rand(1, array_sum($values));

    foreach ($values as $item => $weight) {

        if  ($r <= $weight) return $item;

        $r -= $weight;

    }

}

?>

Enjoy!

bjcffnet at gmail dot com
30-Aug-2005 07:29


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;

}

?>

alexkropivko at(dog) yandex dot ru
16-Jun-2005 09:21


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];

maxnamara at yahoo dot com
13-Mar-2005 07:22


<?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>";

?>

yhoko at yhoko dot com
28-Aug-2004 09:16


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)]; 

?>

leighm at linuxbandwagon dot com leigh morresi
09-Mar-2004 11:36


Another array based password generator, this one is a port from the python mailman version.





this generates slightly predictable but human readable passwords that people can remember


output passwords are for example "rikanumi"





<?php


// port of mailman version


function MakeRandomPassword($length=6) {


$_vowels = array ('a', 'e', 'i', 'o', 'u');    


$_consonants = array ('b', 'c', 'd', 'f', 'g', 'h', 'k', 'm', 'n','p', 'r', 's', 't', 'v', 'w', 'x', 'z');    


$_syllables = array ();    


foreach ($_vowels as $v) {


    foreach ($_consonants as $c) {    


        array_push($_syllables,"$c$v");    


        array_push($_syllables,"$v$c");


    }


}





for ( $i=0;$i<=($length/2);$i++)         $newpass=$newpass.$_syllables[array_rand($_syllables) ];





return $newpass;


?>





}

tim dot meader at gsfc dot nasa dot gov
06-Mar-2004 10:31


Just thought I would contribute a password generation function 


that uses array_rand. I wrote this because I 


could not find anywhere a PHP equivalent of the ability 


that the String::Random module in Perl has, which allows 


you to specify a schema for how you want the random 


string created. In other words: I want 2 Uppercase, 3 


lowercase, 2 intergers...etc.  This isn't too comprehensive, 


notably it doesn't account for one choosing more itterations


 of a particular type than there are in the array (ie - 


choosing more than 10 numbers from output). Additionally, 


this doesn't allow for any repeated characters. Hope it can 


be of use... comments appreciated.





<?php


    function &doGeneratePasswords()


    {


        //////////////////////////////////////


        // lowercase L left out for clarity //


        //////////////////////////////////////


        $l_achLowercase = array("a","b","c","d","e","f","g","h",


                                  "i","j","k","m","n","o","p","q",


                                  "r","s","t","u","v","w","x",


                                  "y","z");


        $l_iNumLowercase = count($l_achLowercase);





        ////////////////////////////////////////////


        // uppercase I and O left out for clarity //


        ////////////////////////////////////////////


        $l_achUppercase = array("A","B","C","D","E","F","G","H",


                                  "J","K","L","M","N","P","Q",


                                  "R","S","T","U","V","W",


                                  "X","Y","Z");


        $l_iNumUppercase = count($l_achUppercase);





        $l_aiNumbers = array("1","2","3","4","5","6","7","8","9","0");


        $l_iNumNumbers = count($l_aiNumbers);





        $l_achSpecialChars = array("!","#","%","@","*","&");


        $l_iNumSpecialChars = count($l_achSpecialChars);





        ///////////////////////////////////////////////////////////////////


        // Make sure to create enough blank spaces as you want passwords //


        ///////////////////////////////////////////////////////////////////


        $l_astPasswds = array("","","","");





        //////////////////////////////////////////


        // Hopefully these are self explanatory //


        //////////////////////////////////////////


        $l_astPasswdSchemes = array("SLUUSLNN","LSUNLLNU","NNUSLLSN","LNLSUNLU");





        $l_iNumPasswds = count($l_astPasswdSchemes);





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


            $l_iSchemeLength = strlen($l_astPasswdSchemes[$i]);





            $l_achRandLowercase = array_values(array_rand($l_achLowercase, $l_iNumLowercase));


            $l_achRandUppercase = array_values(array_rand($l_achUppercase, $l_iNumUppercase));


            $l_aiRandNumbers = array_values(array_rand($l_aiNumbers, $l_iNumNumbers));


            $l_achRandSpecialChars = array_values(array_rand($l_achSpecialChars, $l_iNumSpecialChars));





            for ($j=0; $j < $l_iSchemeLength; $j++) {


                $l_chCurrentOne = $l_astPasswdSchemes[$i]{$j};





                switch ($l_chCurrentOne) {


                    case "L":


                        $l_astPasswds[$i] .= $l_achLowercase[array_shift($l_achRandLowercase)];


                        break;





                    case "U":


                        $l_astPasswds[$i] .= $l_achUppercase[array_shift($l_achRandUppercase)];


                        break;





                    case "N":


                        $l_astPasswds[$i] .= $l_aiNumbers[array_shift($l_aiRandNumbers)];


                        break;





                    case "S":


                        $l_astPasswds[$i] .= $l_achSpecialChars[array_shift($l_achRandSpecialChars)];


                        break;





                    default:


                        break;


                }


            }


        }





        return $l_astPasswds;


    }


?>

jpinedo
02-Nov-2003 05:15


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";


?>

wazaawazaa600 at msn dot com
16-Oct-2003 03:24


The function go well ever that you work with a simple array. An array of arrays (also called a table), not works with the function correctly. Example:





<?php


$a=array(array(0,1),array(1,2),array(2,3),array(3,4),array(4,5));


echo $a[0][0];echo"<br>";


echo $a[1][0];echo"<br>";





$b=array_rand($a,2);


echo $b[0][0];echo"<br>"; //This writes nothing


echo $b[1][0];echo"<br>"; //This writes nothing


?>





If you are in this situation, you will need to make your own solution.

asarnoNOSPAM@interbaun DOT com
24-Jun-2003 02:06


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.

c at aufbix dot org
14-Jun-2003 04:31


If you use array_rand with num_req=1, it will return an integer, and not an array as it would in all other circumstances. You can bypass that like this:





<?php


$randelts=array_rand($feeds,$num);





for ($j=0;$j<count($randelts);$j++) {


  if ($num==1) {$subq[$j]=$feeds[$randelts];}


  else {$subq[$j]=$feeds[$randelts[$i]]}


}


?>

Paul Hodel (paul at ue dot com dot br)
18-Apr-2003 04:40


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];

}



?>

scandar at home dot se
14-Apr-2003 12:58


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.

mickoz[at]parodius[dot]com
02-Dec-2002 12:28


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);


?>

dboy at jumpstation dot org
23-Jul-2002 09:58


If you just want to pull one random element from an array, try something like this:





<?php


mt_srand((double) microtime() * 1000000);


$myarray = array("this", "is", "a",


                 "test", "to", "see",


                 "if", "I", "can",


                 "pull", "one", "element",


                 "from", "an", "array",


                 "randomly");


$random_index = mt_rand(0, (count($myarray)-1));


?>





Then to test the randomness or what have you try a simple:





<?php


$string = ""; // Just to kill the warning


for ($i=0; $i<count($myarray); $i++) {


     $random_index = mt_rand(0, (count($myarray)-1));


     $string .= "$myarray[$random_index] ";


}


$string = rtrim($string);


echo ($string);


?>





I've gotten extremely good output from this method and would recommend it if you're just pulling one element.

josh at 3io dot com
15-Jun-2002 06:20


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];


}


?>

uvm at sun dot he dot net
10-Jul-2001 09:09


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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