<?php
//the current array and an empty new array to get the result.
$cur_array = [0 => "4,9", 1 => "5,9"];
$new_array = [];
 
//run through all array values to convert these.
for ($i = 0; $i < count($cur_array); $i++) {
 
    //get an array of the comma separated list.
    $part = explode(',', $cur_array[$i]);
 
    //add the array of comma separated list to the new array (result).
    $new_array = array_merge($new_array, $part);
}
 
//convert all string values to integer values.
for ($j = 0; $j < count($new_array); $j++) {
    $new_array[$j] = intval($new_array[$j]);
}
 
//output of the new array (debug).
var_dump($new_array);

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