Glob and group file names in PHP

Question

Suppose there is a folder in the server called "mp3" with plenty of mp3 files, "a1.mp3", "a2.mp3", "a3.mp3", "a4.mp3", "ao0.mp3", "ao2.mp3", "ao3.mp3", "ci1.mp3", "ci2.mp3" etc.

    foreach (glob('sound/*.mp3') as $filename) {
        if (!in_array($filename,$exclude_files)) {
            $outputtext .= "<p>".preg_replace('/\\.[^.\\s]{3,4}$/', '', basename($filename))."</p>";
        }
    }echo $outputtext;

My source code is as above and the current result is:

a1
a2
a3
ao0
ao2
ao3
ci1
ci2

But the result what I want is to group all same patterns as follows:

a - 123
ao - 023
ci - 12

Thanks for all your reply.

Answer 1

    foreach (glob($path.'*.mp3') as $filename) {
        if (!in_array($filename,$exclude_files)) {
            if (preg_match('/[0-9]/', $filename, $matches, PREG_OFFSET_CAPTURE)) {
                // Starting after "sound/", so the starting position is 6
                $filenamestr[$n] = substr($filename, 6, $matches[0][1]-6+1);
                $n++;
            }
        }
    }

    $totalfiles = $n--;
    $mp3 = "";
    $o = 0;
    $p = 0;
    for ($l = 0; $l < $totalfiles; $l++) {
        if (substr($filenamestr[$l], 0, strlen($filenamestr[$l])-1) == substr($filenamestr[$l-1], 0, strlen($filenamestr[$l-1])-1)) {
            // Connect file names to an array when current file name is the same as previous one
            $p++;
            $mp3file[$o][$p] = substr($filenamestr[$l], -1);
            $mergemp3file[$o] .= $mp3file[$o][$p];
        } else {
            // Produce another array for file name when current file name is different from previous one
            $o++;
            $p = 0;
            $mp3file[$o][$p] = substr($filenamestr[$l], 0, strlen($filenamestr[$l])-1)." - ".substr($filenamestr[$l], -1);
            // Collect sound files for each file name
            $mergemp3file[$o] .= $mp3file[$o][$p];
        }
    }

    // Generate merged sound files for each file name
    $totalmp3 = $o--;
    for ($o = 1; $o < $totalmp3; $o++) {
        $outputtext .= "<br/>".$mergemp3file[$o].chr(13);
    }