html - Random range without duplicates in PHP

Question

I have 60 images but I want to randomly show 20 from 1 to 60.

My code is something like this, it shows 60

<?php
  for( $i = 1; $i < 61; $i++ ) 
    { 
       print '<a href="javascript:;"><img src="images/items/' . $i . '.png"  class="allitems item' . $i . '" /></a>'; 
    }    
?>

I found PHP function RAND(), but unable to implement, any help would be appreciated.

Answer 1

Try functions range() and array_rand():

<?php
// range generates array with direct sequence from 1 to 60 (inclusive).
// array_rand extracts 20 random keys from it.
$range = array_rand(range(1, 60), 20);

while(count($range)){
    $i = array_shift($range) + 1;

    print '<a href="javascript:;"><img src="images/items/' . $i . '.png"  class="allitems item' . $i . '" /></a>';
}
?>

---

UPDv1: With for-loop:

<?php
$range = array_rand(range(1, 60), 20);

for($i = 0; $i < 20; $i++){
    $image = $range[$i] + 1;

    print '<a href="javascript:;"><img src="images/items/' . $image . '.png"  class="allitems item' . $image . '" /></a>';
}

unset($range, $i, $image);
?>

---

UPDv2:

I've misread array_rand()s manual. It returns array keys instead of elements. Here is multipurpose version (fix with array_flip()):

<?php
header('Content-Type: text/plain');

$buffer = range(1, 60);
$buffer = array_flip($buffer);
$buffer = array_rand($buffer, 20);

foreach($buffer as $value){
    echo $value, PHP_EOL;
}
?>

And a shortcut function (negatives safe, and overall count safe):

<?php
header('Content-Type: text/plain');

function random_range($min, $max, $count){
    $count = abs((int)$count);

    if($min > $max){
        list($min, $max) = array($max, $min);
    }

    $uniques = abs($max - $min);

    if($count > $uniques)$count = $uniques;

    return array_rand(array_flip(range($min, $max)), $count);
}

foreach(random_range(1, 60, 20) as $value){
    echo $value, PHP_EOL;
}
?>

---

There is another way for those, who needs non-growing random sequence. Use this:

<?php
header('Content-Type: text/plain');

function random_range($min, $max, $count){
    $count = abs((int)$count);

    if($min > $max){
        list($min, $max) = array($max, $min);
    }

    $uniques = abs($max - $min);

    if($count > $uniques)$count = $uniques;

    $result = array();
    $ready  = 0;

    while($ready < $count){
        $buffer = rand($min, $max);

        if(!in_array($buffer, $result)){
            $result[] = $buffer;
            $ready++;
        }
    }

    return $result;
}

foreach(random_range(1, 60, 20) as $value){
    echo $value, PHP_EOL;
}
?>

---

UPDv3:

Another way, used range() + shuffle() + array_slice():

<?php
header('Content-Type: text/plain');

function random_range($min, $max, $count){
    $count = abs((int)$count);

    if($min > $max){
        list($min, $max) = array($max, $min);
    }

    $uniques = abs($max - $min);

    if($count > $uniques)$count = $uniques;

    $result = range($min, $max);
    shuffle($result);

    return array_slice($result, 0, $count);
}

foreach(random_range(5, 20, 5) as $random){
    echo $random, ' ';
}
?>