$re = '/\b(?=(?:[a-zA-Z]\d+[a-zA-Z]*)|(?:\d+[a-zA-Z]\d*))[a-zA-Z0-9]*/m';
$str = '1921 abc abc abc 1k
4320 abcs abc Apt 201b
1250 abcd Ave Apt 3c
61a abcd Ave
1b abcd Ave
39r abcd Rd
16w750 abcd Ave
a123def';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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