array_reduce ( array, callbackfunction [, int $initial] );

<?php
   function call_back_function(v1,v2) {
      return v1 . "-" .v2;
   }

   input = array("a"=>"banana","b"=>"apple","c"=>"orange");

   print_r(array_reduce(input, call_back_function));
   print_r("<br />");
   print_r(array_reduce($input, call_back_function, 10));
?>

-banana-apple-orange
10-banana-apple-orange