PHPで文字列に文字が出現する回数を見つけるプログラム

<?php
   $str = "welcome to tutorials point";
   $str = str_replace(" ","",$str);
   $arr = str_split($str);
   foreach ($arr as $key =>$val){
      if (!isset($output[$val])){
            $output[$val] = 1;
      }
      else{
         $output[$val] += 1;
      }
   }
   foreach($output as $char =>$number){
      echo $char." ".'appears '. $number." ".'times'."\n";
   }
?>

出力

w appears 1 times
e appears 2 times
l appears 2 times
c appears 1 times
o appears 4 times
m appears 1 times
t appears 4 times
u appears 1 times
r appears 1 times
i appears 2 times
a appears 1 times
s appears 1 times
p appears 1 times
n appears 1 times