PHP: split a string of alternating groups of characters into an array

Question

I have a string whose correct syntax is the regex ^([0-9]+[abc])+$. So examples of valid strings would be: '1a2b' or '00333b1119a555a0c'

For clarity, the string is a list of (value, letter) pairs and the order matters. I'm stuck with the input string so I can't change that. While testing for correct syntax seems easy in principle with the above regex, I'm trying to think of the most efficient way in PHP to transform a compliant string into a usable array something like this:

Input:

'00333b1119a555a0c'

Output:

array (
  0 =>  array('num' => '00333', 'let' => 'b'),
  1 =>  array('num' => '1119', 'let' => 'a'),
  2 =>  array('num' => '555', 'let' => 'a'),
  3 =>  array('num' => '0', 'let' => 'c')
)

I'm having difficulty using preg_match for this. For example this doesn't give the expected result, the intent being to greedy-match on EITHER \d+ (and save that) OR [abc] (and save that), repeated until end of string reached.

$text = '00b000b0b';
$out = array();
$x = preg_match("/^(?:(\d+|[abc]))+$/", $text, $out);

This didn't work either, the intent here being to greedy-match on \d+[abc] (and save these), repeated until end of string reached, and split them into numbers and letter afterwards.

$text = '00b000b0b';
$out = array();
$x = preg_match("/^(?:\d+[abc])+$/", $text, $out);

I'd planned to check syntax as part of the preg_match, then use the preg_match output to greedy-match the 'blocks' (or keep the delimiters if using preg_split), then if needed loop through the result 2 items at a time using for (...; i+=2) to extract value-letter in their pairs.

But I can't seem to even get that basic preg_split() or preg_match() approach to work smoothly, much less explore if there's a 'neater' or more efficient way.

Answer 1

Your regex needs a few matching groups

/([0-9]+?)([a-z])/i

This means match all numbers in one group, and all letters in another. Preg match all gets all matches.

The key to the regex is the non greedy flag ? which matches the shortest possible string.

match[0] is the whole match
match[1] is the first match group (the numbers)
match[2] is the second match group (the letter)

example below

<?php
$input = '00333b1119a555a0c';

$regex = '/([0-9]+?)([a-z])/i';

$out = [];

$parsed = [];

if (preg_match_all($regex, $input, $out)) {
    foreach ($out[0] as $index => $value) {
        $parsed[] = [
            'num' => $out[1][$index],
            'let' => $out[2][$index],
        ];
    }
}

var_dump($parsed);

output

array(4) {
  [0] =>
  array(2) {
    'num' =>
    string(5) "00333"
    'let' =>
    string(1) "b"
  }
  [1] =>
  array(2) {
    'num' =>
    string(4) "1119"
    'let' =>
    string(1) "a"
  }
  [2] =>
  array(2) {
    'num' =>
    string(3) "555"
    'let' =>
    string(1) "a"
  }
  [3] =>
  array(2) {
    'num' =>
    string(1) "0"
    'let' =>
    string(1) "c"
  }
}

Answer 2

Simple solution with preg_match_all(with PREG_SET_ORDER flag) and array_map functions:

$input = '00333b1119a555a0c';

preg_match_all('/([0-9]+?)([a-z]+?)/i', $input, $matches, PREG_SET_ORDER);
$result = array_map(function($v) {
    return ['num' => $v[1], 'let' => $v[2]];
}, $matches);

print_r($result);

The output:

Array
(
    [0] => Array
        (
            [num] => 00333
            [let] => b
        )

    [1] => Array
        (
            [num] => 1119
            [let] => a
        )

    [2] => Array
        (
            [num] => 555
            [let] => a
        )

    [3] => Array
        (
            [num] => 0
            [let] => c
        )
)