metodo per filtrare nome di un file

[cubalibre810]

<?php
$array = array("PE1.1_fn0",
"PE1.2_fn0",
"PE1.3_fn0",
"PE1.4_fn0",
"PE1.5_fn0",
"PE2.3_fn0",
"PE2.4_fn0",
"PE2.5_fn0",
"PE2.6_fn0",
"PE3.1_fn0",
"PE5.4_fn0",
"PE5.1_fn0",
"AB1.1_fn0",
"AB1.2_fn0",
"AB1.3_fn0",
"AB2.1_fn0",
"AB2.2_fn0",
"AB2.3_fn0",
"AB2.4_fn0",
"A1.1_fn0",
"A1.2_fn0",
"A1.3_fn0",
"A1.4_fn0",
"A2.7_fn0",
"A3.1_fn0",
"A3.2_fn0",
"A3.3_fn0",
"A_fn0",
"A_fn1",
"A_fn2",
"B_fn1",
"C_fn1",
"C_fn2",);

$keys = array();

foreach($array as $each)
{
    $prefix = preg_replace("([^A-Z\.]+)", "x", array_shift(explode("_", $each)));
    $keys[] = $prefix;
}

print "<pre>";
print_r(array_count_values($keys));

?>