Draw with different percentages

Question

I have a "box open" system, which works as follows:

The box can have X items (as much as you want) where each item will have Y% to be earned, being: # or #.1% (no more decimal places)

That is: the "Box one" can have 10 items, where:

1. 0.5% of beverage earned
2. 1% chance of being won
3. 4% chance of being won
4. 4.5% chance of being won
5. 5% chance of being won
6. 15% of being won
7. 15% of being won
8. 15% of being won
9. 20% chance of being won
10. 20% chance of being won

Always the winning percentage sum of the items will be 100% round

Currently, I only have a simple function that takes any item from the array of items in the box:

$vencedor = $items[array_rand($items)];

And he brings me the "drawn" item, what I need is for the percentage of each item to be taken into account, and I’m not getting it

I tried some things, none arrived at the desired result

Answer 1

The solution proposed by @bfavaretto in the comments works perfectly. Here’s another suggestion if you couldn’t solve it.

I made a solution based on a range of numbers that each element can have. The higher the chance percentage, the greater the range of numbers of each element. Based on your example, I created the following array:

$items = array(

    "Item 1" => 0.5, // porcentagens
    "Item 2" => 1,
    "Item 3" => 4,
    "Item 4" => 4.5,
    "Item 5" => 5,
    "Item 6" => 15,
    "Item 7" => 15,
    "Item 8" => 15,
    "Item 9" => 20,
    "Item 10" => 20

);

With this, a new array is generated with the name of each element and its respective ranges through this code:

$valor = 1000; // valor do peso máximo e total dos itens
$inicio = 1;
$ultimo_valor = 0;

$array_elementos = array(); // array para sorteio

// cria o array para sorteio
foreach($items as $nome => $porcentagem){

    $val =  ($valor * $porcentagem) / 100;
    $valorFinal = $val + $inicio - 1;
    $array_elementos[$nome] = $inicio."-".$valorFinal;
    $inicio = $valorFinal + 1;

}

See how the array looks $array_elementos:

Array ( 

    [Item 1] => 1-5 
    [Item 2] => 6-15 
    [Item 3] => 16-55 
    [Item 4] => 56-100 
    [Item 5] => 101-150 
    [Item 6] => 151-300 
    [Item 7] => 301-450 
    [Item 8] => 451-600 
    [Item 9] => 601-800 
    [Item 10] => 801-1000 

)

Now just draw a random number and search the array in which element the number is in. So:

// numero randômico "sorteio"
// de 1 até o valor máximo
$num_rand = rand(1, $valor);

$elemento_sorteado = "";

// procura o elemento sorteado
foreach($array_elementos as $nome => $peso){
    $valores = explode("-", $peso);
    if($num_rand >= $valores[0] && $num_rand <= $valores[1]){
        $elemento_sorteado = $nome;
        break;
    }
}

echo $elemento_sorteado;

See the code working on ideone