Splitting a string using lookback in PHP - php

Question

I have a product feed where the product options is formatted like this:
Color{1} : Black[14], White[42] Size{2} : Small[16], Medium[17], Large[18]
For my script to understand and parse the product options correctly, it needs to be in the following format:
Color:Black,White|Size:Small,Medium,Large
I started out like this to remove unnecessary information:
$matches[1] = preg_replace("/\{\d{1,}\} : /", ': ', $matches[1]);
$matches[1] = preg_replace("/\[\d{1,}\]/", '', $matches[1]);
Which gives this output:
Color: Black, White Size: Small, Medium, Large
But my problem now is "how to insert a pipe before the option name, unless its only one option, or the first option". I guess I need to use some sort of lookback, but I have no idea.

Answer 1

First, split the string into several individual options using preg_split():
$arr = preg_split('/\s+(?=[a-z]+{\d+})/i', $str);
(?=[a-z]+{\d+}) is a positive lookahead that asserts that the whitespace (\s+) is followed by a string of the format <string>{xx}. It's used here to pinpoint on which spaces the split should happen. It's important to note that the lookahead assertion is zero-width, i.e. it doesn't consume any characters at all.
Once you have the split array, loop through it, and remove {xx}, [xx] parts and whitespace:
foreach ($arr as &$str)
$str = preg_replace('/(?:{\d+}|\[\d+\]|\s*)/', '', $str);
Join the array by |:
echo join('|', $arr);
Output:
Color:Black,White|Size:Small,Medium,Large
Demo

Answer 2

This method uses only two iterations of regex substitution
First, delete all spaces along with digits
$re = "/(.\\d+.|[ ]+)/";
$str = "Color{1} : Black[14], White[42] Size{2} : Small[16], Medium[17], Large[18]";
$subst = '';
$result = preg_replace($re, $subst, $str);
Then add in the pipe
$re = "/([a-z])([A-Z])/";
$subst = '\1|\2';
$endresult = preg_replace($re, $subst, $result);
Input:
Color{1} : Black[14], White[42] Size{2} : Small[16], Medium[17], Large[18]
Output:
Color:Black,White|Size:Small,Medium,Large
Here's a quick demo
Note: I'm assuming that the digits are always surrounded by a curly brace or a bracket without any spacing in between and that the quantity names are only alpha character (never digits).