<?php
 
$_POST = array(
'items_501' => 2,
'txt_501' =>'Laserjet',
'items_510' => '',
'txt_510' => 'Item Description'
);
$items = [];
foreach($_POST as $key => $value) {
    //$_POST[$key] = filter($value); //POST variables are filtered for bad input
    $x = explode("_", $key);
    $itemno = $x[1];
    if ($x[0] == "txt") { $items[$itemno][1] = $value; }
    elseif ($x[0] == "items") { $items[$itemno][0] = $value; }
}
 
foreach($items as $key => $value) {
	$valuestr = implode(',', $value);
	echo "$key: $valuestr\n";
}

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