exploding a string using a regular expression

Question

I have a string as below (the letters in the example could be numbers or texts and could be either uppercase or lowercase or both. If a value is a sentence, it should be between

Answer 1

You can do the job using preg_match_all

$string="a,b,c,(d,e,f),g,'h, i j.',k";

preg_match_all('~\'[^\']++\'|\([^)]++\)|[^,]++~', $string,$result);
print_r($result[0]);

Explanation:

The trick is to match parenthesis before the ,

~          Pattern delimiter
'
[^']       All charaters but not a single quote
++         one or more time in [possessive][1] mode
'
|          or
\([^)]++\) the same with parenthesis
|          or
[^,]       All characters but not a comma
++
~

if you have more than one delimiter like quotes (that are the same for open and close), you can write your pattern like this, using a capture group:

$string="a,b,c,(d,e,f),g,'h, i j.',k,°l,m°,#o,p#,@q,r@,s";

preg_match_all('~([\'#@°]).*?\1|\([^)]++\)|[^,]++~', $string,$result);
print_r($result[0]);

explanation:

(['#@°])   one character in the class is captured in group 1
.*?        any character zero or more time in lazy mode 
\1         group 1 content

With nested parenthesis:

$string="a,b,(c,(d,(e),f),t),g,'h, i j.',k,°l,m°,#o,p#,@q,r@,s";

preg_match_all('~([\'#@°]).*?\1|(\((?>[^()]++|(?-1)?)*\))|[^,]++~', $string,$result);
print_r($result[0]);