- preg_match_all: documentation ( source)
- var_export: documentation ( source)
<?php
$string = "1A1R0A";
var_export(preg_match_all('~(\d)\K\D~', $string, $out) ? [$out[1], $out[0]] : [[], []]);
echo "\n--- or ---\n";
[$letters, $numbers] = preg_match_all('~(\d)\K\D~', $string, $out) ? $out : [[], []];
var_export($numbers);
echo "\n";
var_export($letters);