Preventing array_rand string duplicate in PHP

Question

I am randomizing php templates to include them in the web page. Each time the user reloads the web page, a new randomized template will appear.

Problem with array_rand it returns one random string each time the user reloads the web page, and the same template may be displayed again and again.

For example, let's say the user reloads the page 3 times. He may get the following templates: template1.php, template1.php, template2.php

I want the user to see all the templates in a random order. For example, template3.php,template2.php,template1.php

$items = array("template1.php","template2.php","template3.php"); #templates array
$a = $items[array_rand($items,1)]; #randomize templates

include $a; #including randomized template

You could use in `if` statement in combination with a `$_SESSION[]` variable to store the previous page and omit the previous page from the array before calling your rand procedure — pokeybit, Apr 30 '18 at 07:34
or maybe to shuffle the templates and store them all in a session? — , Apr 30 '18 at 07:38
"all templates in random order" is the exact definition of [shuffle](http://php.net/shuffle) ;-) But you must decide what you want to happen when you run out of templates. — Álvaro González, Apr 30 '18 at 07:41
Yes but, is it okay that the last template in each run becomes the first template on next run? — Álvaro González, Apr 30 '18 at 07:47

score 1 · Answer 1 · answered Apr 30 '18 at 07:38

1

You could use in if statement in combination with a $_SESSION[] variable to store the previous page and omit the previous page from the array before calling your rand procedure

session_start();
$items = array("template1.php","template2.php","template3.php");
if (($key = array_search($_SESSION['last_page'], $items)) !== false) {
    unset($items [$key]);
} //taken from https://stackoverflow.com/questions/7225070/php-array-delete-by-value-not-key
$a = $items[array_rand($items,1)];
$_SESSION['last_page'] = $a;
include $a;

answered Apr 30 '18 at 07:38

pokeybit

1,032
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1

To make sure all pages are visited at least once before the array is reset, use @Philipp Maurer answer below/above – pokeybit Apr 30 '18 at 07:44
I tried your code but i get same templates before seeing all of them. It doesn't work as required. – Apr 30 '18 at 11:28

Philipp Maurer · Answer 2 · 2018-04-30T09:10:45.953

0

For that to work, you need to save which templates the visitor has already loaded. This can be saved in the session for example:

//At the beginning of your script
session_start();

//... Some code

//Read visited paths from session or create a new list. 
//?? works only in PHP7+. Use isset()?: instead of ?? for previous versions
$visitedTemplates = $_SESSION['visitedTemplates'] ?? [];

//Your list, just slightly changed syntax. Same thing
$originalList = [
    "template1.php",
    "template2.php",
    "template3.php"
];

//Remove all paths that were already visited from the randomList
$randomList = array_diff($originalList, $visitedTemplates);

//You need to check now if there are paths left
if (empty($randomList)) {
    //The user did load all templates

    //So first you set the list to choose a new template from to the list of all templates
    $randomList = $originalList;

    //And then you delete the cache of the visited templates
    $visitedTemplates = [];
}

//Show the user the next one
$randomTemplate = $randomList[array_rand($randomList)];
include $randomTemplate;

//Now we need to save, that the user loaded this template
$visitedTemplates[] = $randomTemplate;

//And we need to save the new list in the session
$_SESSION['visitedTemplates'] = $visitedTemplates;

edited Apr 30 '18 at 09:10

answered Apr 30 '18 at 07:43

Philipp Maurer

2,480
6
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Accept this answer as it fits your edited requirements more than mine – pokeybit Apr 30 '18 at 07:47
@GragasIncoming Yes, i adjusted the answer for it – Philipp Maurer Apr 30 '18 at 07:53
Can you comment a code for php 5 support? `$visitedTemplates = $_SESSION['visitedTemplates'] ?? [];` – Apr 30 '18 at 07:55
@GragasIncoming No, but it is not that challenging to read into the necessary changes based on the comments i already did :-) The information i provided should be enough for you to create a solution. – Philipp Maurer Apr 30 '18 at 07:57
@GragasIncoming Yet, [this answer](https://stackoverflow.com/a/14521011/8913537) is a good start to look into the ternary if operator. – Philipp Maurer Apr 30 '18 at 07:59
what if i replace `??` with `?:` ? – Apr 30 '18 at 08:04
@GragasIncoming Should work in most cases, try it out ;-) – Philipp Maurer Apr 30 '18 at 08:05
Same template is displayed again like i was doing with random. I noticed that there not any sessions stored in browser – Apr 30 '18 at 08:30
@GragasIncoming Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/170069/discussion-between-philipp-maurer-and-gragas-incoming). – Philipp Maurer Apr 30 '18 at 08:41
@GragasIncoming Fixed another typo, should work now. – Philipp Maurer Apr 30 '18 at 09:12

Preventing array_rand string duplicate in PHP

2 Answers2