PHP: sort folder first and then files

Try this :

$dir = '/master/files';
$directories = array();
$files_list  = array();
$files = scandir($dir);
foreach($files as $file){
   if(($file != '.') && ($file != '..')){
      if(is_dir($dir.'/'.$file)){
         $directories[]  = $file;

      }else{
         $files_list[]    = $file;

      }
   }
}

foreach($directories as $directory){
   echo '<li class="folder">'.$directory.'</li>';
}
foreach($files_list as $file_list){
   echo '<li class="file">'.$file_list.'</li>';
}

You don't need to make 2 loops, you can do the job with this piece of code:

<?php

function scandirSorted($path) {

    $sortedData = array();
    foreach(scandir($path) as $file) {

        // Skip the . and .. folder
        if($file == '.' || $file == '..')
            continue;            

        if(is_file($path . $file)) {
            // Add entry at the end of the array
            array_push($sortedData, '<li class="folder">' . $file . '</li>');
        } else {
            // Add entry at the begin of the array
            array_unshift($sortedData, '<li class="file">' . $file . '</li>');
        }
    }
    return $sortedData;
}

?>

This function will return the list of entries of your path, folders first, then files.

Modifying your code as little as possible:

$folder_list = "";
$file_list = "";
$dir = '/master/files';
$files = scandir($dir);
foreach($files as $file){
   if(($file != '.') && ($file != '..')){
      if(is_dir($dir.'/'.$file)){
         $folder_list .= '<li class="folder">'.$file.'</li>';
      }else{
         $file_list .= '<li class="file">'.$file.'</li>';
      }
   }
}

print $folder_list;
print $file_list;

This only loops through everything once, rather than requiring multiple passes.