Shopp Variation Radio Buttons

/**
* This snippet is intended for use in a product.php template
* in the context of Shopp 1.1.9.
*
* Creates radio buttons to allow product variations to be
* selected. Pricing information per-variation is deliberately
* omitted.
*/

$i = 1;

while (shopp('product', 'variations'))
{
    // Form the radio button name
    $id = shopp('product', 'id', 'return=true');
    $name = "products[$id][options][]";

    // The first field should be selected by default
    $selected = ($i == 1) ? 'checked="checked"' : '';

    // Echo to screen
    echo '<input type="radio" name="'.$name.'" value="'.$i.'" '.$selected.' />';
    shopp('product', 'variation', 'label');

    // Increment
    $i++;
}