Building array keys using a span of numbers for like values

Question

I am calculating discounts based on a quantity after 6.

Is there a cleaner way to do this:

$leg_directory_discount = array(
    6   =>  .50,
    7   =>  .50,
    8   =>  .50,
    9   =>  .50,
    10  =>  .50,
    11  =>  1,
    12  =>  1,
    13  =>  1,
    14  =>  1,
    15  =>  1,
    16  =>  1,
    17  =>  1,
    18  =>  1,
    19  =>  1,
    20  =>  1,
    21  =>  1.5,
    22  =>  1.5,
    23  =>  1.5,
    24  =>  1.5,
    25  =>  1.5,
    26  =>  1.5,
    27  =>  1.5,
    28  =>  1.5,
    29  =>  1.5,
    30  =>  1.5,
    31  =>  1.5,
    32  =>  1.5,
    33  =>  1.5,
    34  =>  1.5,
    35  =>  1.5,
    36  =>  1.5,
    37  =>  1.5,
    38  =>  1.5,
);

edit: The max and min values of the discounts never change. Here is how I'm calculating the discount and arriving at the final price:

if($v[0]['leg_discount'] == '1' && $v[0]['qty'] >= 6){
    $discount = $qty * $leg_directory_discount[$qty];
    $price = $price - $discount;
}

Answer 1

Some simple logic will save you from all that (error-prone) writing. For instance:

if ($qty >= 6)
{
    if ($qty >= 21)
        $leg_directory_discount = 1.5;
    elseif ($qty >=11)
        $leg_directory_discount = 1.0;
    else
        $leg_directory_discount = 0.5;
}
else
    $leg_directory_discount = 0.0;

Answer 2

I like the idea of putting the discount steps into an array, but stating a discount for every possible quantity seems too much.

$leg_directory_discount = array(
    0 => 0,
    6   =>  .50,
    11  =>  1,
    21  =>  1.5,
);

This is the discount configuration - can later be stored in a config file or database.

This function gets the discount to be used:

function getDiscount($qty, $leg_directory_discount) {
  $return = 0;
  foreach ($leg_directory_discount as $amount => $discount) {
    if ($qty >= $amount) {
      $return = $discount;
    }
  }
  return $discount;
}

Answer 3

You could use a switch statement as well:

switch (true) {
    case ($price <=5):
         $discount = 0.0;
         break;
    case ($price <= 10):
         $discount = 0.5;
         break;
    case ($price <= 20):
         $discount = 1.0;
         break;
    default:
         $discount = 1.5;
         break;
}

Also your final price could be reduced to $price = $price * (100 - $discount) / 100;