Question

In my php script, I have a variable $data that contains an array that may have various number of elements.

The script picks one of the array elements at random and outputs it to the browser:

# count number of elements in $data
$n = count($data);

# pick a random number out of the number of elements in $data
$rand = rand(0, ($n - 1));

# output a random element
echo '<p> . trim($data[$rand]) . '</p>';

QUESTION: I want to improve that script, so that it doesn’t output the same array element again until it runs out of array elements. For example, if an array contains elements numbered 0 to 9, and the script picked an array element #4, I want it to remember that, and next time the script runs, to exclude the element that was #4.

It could probably be done in many different ways, but I’m looking for the simplest and most elegant solution, and would be grateful for help from a PHP expert.

Answer 1

Save the numbers that were already picked in the user’s session.

session_start();
$n = count($data); 

// If the array isn't initialized, or we used all the numbers, reset the array
if( !isset( $_SESSION['used_nums']) || count( $_SESSION['used_nums']) == $n) {
    $_SESSION['used_nums'] = array();
}

do{ 
    $rand = rand(0, ($n - 1));
} while( isset( $_SESSION['used_nums'][$rand]));

echo '<p>' . trim($data[$rand]) . '</p>';    
$_SESSION['used_nums'][$rand] = 1;

---

Or, perhaps a more clever way, using array_intersect_key and array_rand:

session_start();
$n = count($data); 

// If the array isn't initialized, or we used all the numbers, reset the array
if( !isset( $_SESSION['used_nums']) || count( $_SESSION['used_nums']) == $n) {
    $_SESSION['used_nums'] = array();
}

$unused = array_intersect_key( $data, $_SESSION['used_nums'];
$rand = array_rand( $unused);

echo '<p>' . trim($unused[$rand]) . '</p>';    
$_SESSION['used_nums'][$rand] = 1;