<?php
$string = '1-350,9-390.99';
$array = explode(',',$string);
$new_array = array();

array_walk($array,'walk', &$new_array);

function walk($val, $key, $new_array){
    $nums = explode('-',$val);
    $new_array[$nums[0]] = $nums[1];
}
print_r($new_array);

?>