here's an example, rather messy but it is late...
Code:
<?php
$sa = "a | 10 15";
$sb = "b | 10 13";
print "a: '".$sa."'<br>";
print "b: '".$sb."'<br>";
print "<br>\n";
$a = split(" ", $sa);
print_r($a);
$b = split(" ", $sb);
print "<br>\n";
print "Therefore:<br>\n";
$sc = ($a[3] > $b[3]) ? ($sa) : ($sb);
print "c: '".$sc."'<br>";
?>