Convert string to array at different character occurence - php

Question

Consider I have this string 'aaaabbbaaaaaabbbb' I want to convert this to array so that I get the following result
$array = [
'aaaa',
'bbb',
'aaaaaa',
'bbbb'
]
How to go about this in PHP?

Answer 1

PHP code demo
Regex: (.)\1{1,}
(.): Match and capture single character.
\1: This will contain first match
\1{1,}: Using matched character one or more times.
<?php
ini_set("display_errors", 1);
$string="aaaabbbaaaaaabbbb";
preg_match_all('/(.)\1{1,}/', $string,$matches);
print_r($matches);
Output:
Array
(
[0] => Array
(
[0] => aaaa
[1] => bbb
[2] => aaaaaa
[3] => bbbb
)
[1] => Array
(
[0] => a
[1] => b
[2] => a
[3] => b
)
)
Or:
PHP code demo
<?php
$string="aaaabbbaaaaaabbbb";
$array=str_split($string);
$start=0;
$end= strlen($string);
$indexValue=$array[0];
$result=array();
$resultantArray=array();
while($start!=$end)
{
if($indexValue==$array[$start])
{
$result[]=$array[$start];
}
else
{
$resultantArray[]=implode("", $result);
$result=array();
$result[]=$indexValue=$array[$start];
}
$start++;
}
$resultantArray[]=implode("", $result);
print_r($resultantArray);
Output:
Array
(
[0] => aaaa
[1] => bbb
[2] => aaaaaa
[3] => bbbb
)

Answer 2

I have written a one-liner using only preg_split() that generates the expected result with no wasted memory (no array bloat):
Code (Demo):
$string = 'aaaabbbaaaaaabbbb';
var_export(preg_split('/(.)\1*\K/', $string, 0, PREG_SPLIT_NO_EMPTY));
Output:
array (
0 => 'aaaa',
1 => 'bbb',
2 => 'aaaaaa',
3 => 'bbbb',
)
Pattern:
(.) #match any single character
\1* #match the same character zero or more times
\K #keep what is matched so far out of the overall regex match
The real magic happens with the \K, for more reading go here.
The 0 parameter in preg_split() means "unlimited matches". This is the default behavior, but it needs to hold its place in the function so that the next parameter is used appropriately as a flag
The final parameter is PREG_SPLIT_NO_EMPTY which removes any empty matches.
Sahil's preg_match_all() method preg_match_all('/(.)\1{1,}/', $string,$matches); is a good attempt but it is not perfect for two reasons:
The first issue is that his use of preg_match_all() returns two subarrays which is double the necessary result.
The second issue is revealed when $string="abbbaaaaaabbbb";. His method will ignore the first lone character. Here is its output:
Array (
[0] => Array
(
[0] => bbb
[1] => aaaaaa
[2] => bbbb
)
[1] => Array
(
[0] => b
[1] => a
[2] => b
)
)
Sahil's second attempt produces the correct output, but requires much more code. A more concise non-regex solution could look like this:
$array = str_split($string);
$last = "";
foreach ($array as $v) {
if (!$last || strpos($last, $v) !== false) {
$last .= $v;
} else {
$result[] = $last;
$last = $v;
}
}
$result[] = $last;
var_export($result);