asort(array [,sort_flags]) sorts an associative array in ascend order by values.

<?PHP
	$arr=array("1"=>"Carbon","2"=>"carbon","3"=>"Protein", "4"=>"fat",);
    asort($arr, SORT_STRING);
	foreach($arr as $key=>$val) echo "$key, $val; "; 
    //1, Carbon; 3, Protein; 2, carbon; 4, fat;
?>

The sort can be modified by sort_flags which include:
  • SORT_REGULAR: sort normally
  • SORT_NUMERIC: sort numerically
  • SORT_STRING: sort as strings
  • SORT_LOCALE_STRING: sort as strings based on the current locale
  • SORT_NATURAL: sort as strings using "natural ordering"
  • SORT_FLAG_CASE: combined with SORT_STRING or SORT_NATURAL to sort case insensitively

Sort by string and case insensitive.

<?PHP
 	$arr=array("1"=>"Carbon","2"=>"carbon","3"=>"Protein", "4"=>"fat",);
    asort($arr, SORT_STRING | SORT_FLAG_CASE);
	foreach($arr as $key=>$val) echo "$key, $val; "; 
    //1, Carbon; 2, carbon; 4, fat; 3, Protein; 
?>

arsort() sorts an associative array in descend order by values.

<?PHP
	$arr=array("1"=>"Carbon","2"=>"carbon","3"=>"Protein", "4"=>"fat",);
    arsort($arr, SORT_STRING | SORT_FLAG_CASE);
	foreach($arr as $key=>$val) echo "$key, $val; "; 
	//3, Protein; 4, fat; 2, carbon; 1, Carbon; 
?>

Following code can sort all the files in a directory by file size.

<?PHP
	function allfiles($dir, $prefix = '')
	{
		$dir = rtrim($dir, '\\/');
		$result = array();
		foreach (scandir($dir) as $f) {
		  if ($f !== '.' and $f !== '..') {
			if (is_dir("$dir\\$f")) {
			  $result = array_merge($result, allfiles("$dir\\$f", "$prefix$f\\"));
			} else {
			  $result[] = $prefix.$f;
			}
		  }
		}
		return $result;
	}

	$dir = "used_files/";
	$files = allfiles($dir);
	$arrsizes = array();
	foreach ($files as $file)
	{
		$arrsizes[$file] = filesize($dir.$file);
	}
	arsort($arrsizes, SORT_NUMERIC); //from largest size to smallest size
	//asort($arrsizes, , SORT_NUMERIC); //reverse
	$files = array_keys($arrsizes);
?>