$re = '/(?P<Flat>([A-Za-z0-9\/\-]*\w\s*)*)(\,|\s|\|)*(?P<Building>([A-Za-z0-9\s\/\-]*\w\s*)(\,|\s)*)(?P<OtherPart>([A-Za-z\s\/\-\,]*\w\s*)(\,|\s)*)(?P<PinCode>([0-9]{6}))/m';
$str = '168-B-A-3, LIG Flats, yur Vihar Phase-3, Vasundhra nclave, East Delhi, Vasundhra nclave, Delhi, 110096';
$subst = "\1\2 \3";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php