TalkPHP - Random Items without a Database

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Random Items without a Database

If you ever wanted to show something random without using the database then this is a decent method:

php Code:

<?php
$banner[]=array("image.gif","http://domain.com/");  
$banner[]=array("image2.gif","http://www.domain.domain.co.uk/");
$banner[]=array("image3.gif","http://search.mysearch.com");

$rand = rand(0,count($banner)-1);  
?>
<p align="center">  
<a href=<?=$banner[$rand][1]?>><img src="<?=$banner[$rand][0]?>" alt="" width="468" height="60" border="0"></a>
</p>

More of a little script than a tutorial, thanks :)

Good tip! There is also the array_rand way. However, as I was trying it just now, it seems to love its zeros, so I decided to do a little test as well. This is the array_rand code:

php Code:

$aFilms = array("V For Vendetta", "Requiem For A Dream", "Jacob's Ladder");
echo $aFilms[array_rand($aFilms)];

And this is my test code as it appeared to be quite fond of returning zero:

php Code:

$aCount = array(0, 0, 0);
$aFilms = array("V For Vendetta", "Requiem For A Dream", "Jacob's Ladder");

for($iIndex = 0; $iIndex <= 5000; $iIndex++)
{
    $aCount[array_rand($aFilms)]++;
}

print_r($aCount);

Results were quite surprising as I thought zero would have been much more dominant:

Quote:

Array
(
[0] => 1701
[1] => 1637
[2] => 1663
)

That looks pretty cool, did a test (10,000 times in a loop):
rand();
Result 1: Page generated in 1.496 seconds.
Result 2: Page generated in 1.400 seconds.
Result 3: Page generated in 1.486 seconds.

array_rand();
Result 1: Page generated in 0.087 seconds.
Result 2: Page generated in 0.078 seconds.
Result 3: Page generated in 0.076 seconds.

Didn't realise the results would vary so much.

That is rather surprising, actually. I'd have thought rand would have been faster. In fact, I was under the impression that the array_rand function would have been a wrapper for the rand function, with 1 or 2 adaptations in that it recognised the array's upper boundary by calling the count function as well.

My favorite way of doing this is to use the shuffle function, to use the example from above:

PHP Code:


		
			
$banner = array();

$banner[]=array("image.gif","http://domain.com/");  

$banner[]=array("image2.gif","http://www.domain.domain.co.uk/");

$banner[]=array("image3.gif","http://search.mysearch.com");

shuffle($banner);



$numBanners = 1;

for ($i=0; $i<$numBanners; $i++) {

  print "".$banner[$i][0];

}

This way you won't duplicate ads if you are showing more than one at a time. I haven't tested its efficiency, but since you randomize the array once I'm guessing its pretty efficient.

Mubs

Interesting, Mubs. The only resevation I'd have about using the array_shuffle function is that it alters the arrangement of the items in the array permanantly. IE: you cannot return them to their previous state unless of course one of the *sort* functions does it - for which you would have needed to construct the array into some sort of arrangement to begin with, such as alphabetical.

Agreed, in my case I didn't need to re-sort just randomize and display so no problems there.

If its a short, simple array, it's easy to just make a copy of the array for randomizing and leave the original sorted as you need.

Mubs

My way of outputing a random logo

PHP Code:


		
			
function random_logo() {



    $szLogo[0] = "mb_v6_logga_800x150.jpg";

    $szLogo[1] = "mb_v6_logga_800x150_2.jpg";

    $szLogo[2] = "mb_v6_logga_800x150_3.jpg";

    $szLogo[3] = "mb_v6_logga_800x150_4.jpg";

    $szLogo[4] = "mb_v6_logga_800x150_5.jpg";

    $szLogo[5] = "mb_v6_logga_800x150_6.jpg";

    $szLogo[6] = "mb_v6_logga_800x150_7.jpg";

    $szLogo[7] = "mb_v6_logga_800x150_8.jpg";

    $szLogo[8] = "mb_v6_logga_800x150_9.jpg";

    $szLogo[9] = "mb_v6_logga_800x150_10.jpg";

    $szLogo[10] = "mb_v6_logga_800x150_11.jpg";

    $szLogo[11] = "mb_v6_logga_800x150_12.jpg";



$szNumber_of_logos = count($szLogo);

$iRand_nr = mt_rand(0, $szNumber_of_logos);

$szRandomLogo = $szLogo[$iRand_nr];



// If no logo is returned use a standard one

if ($szRandomLogo == "") {

    $szRandomLogo = "mb_v6_logga_800x150.jpg";

}

    return $szRandomLogo;



}

This is a little function i wrote quickly for a website i had a few years ago, were i wanted to show a random header with the site logo. It´s not wery effecient i guess neither does it check that the file is actually there so theres room for improvement.

what it does is just return a filename of a logo to display.

Tried to apply your prefered variable namning convention :D

Hope it give someone ispiration.

Can´t remember why i numbered the array thoug.

Excuse the newbie, but isn't it best practice to seed the random function before calling?

You're right in a way, but I believe they now seed automatically before spitting you out a number. As of around PHP version 4.2.0, apparently. Before 4.2.0 though you most certainly would seed the number.

Quote:

Originally Posted by php.net

Note: As of PHP 4.2.0, there is no need to seed the random number generator with srand() or mt_srand() as this is now done automatically.

Just read that off php.net... should've checked first, my bad. :-$

The funny thing is, when I was a PHP beginner, and maybe even an intermediate as well, I used PHP versions earlier than 4.2.0, and I never remember seeding before I output a random value. Oooops!?