- substr: documentation ( source)
- var_dump: documentation ( source)
- array_reduce: documentation ( source)
<?php
$arr = [
"string text 123",
"string text 100",
"string text 555",
];
var_dump(array_reduce($arr, function(array $carry, string $value): array {
$prefix = substr($value, 0, 12);
$carry[$prefix][] = $value;
return $carry;
}, []));