<?php
for ($i=0;$i<5;$i++) {
    $arr[]=$i;
}
$j1=json_encode($arr);
unset($arr[3]);
$j2=json_encode($arr);

echo "$j1\n$j2\n-------\n";
print_r(json_decode($j1));
print_r(json_decode($j2));
echo "------\n";
print_r(json_decode($j1,true));
print_r(json_decode($j2,true));