filter_array() - return a selective sub-array
mixed *filter_array( mixed *arr, string fun, object ob,
mixed extra, ... );
mixed *filter_array( mixed *arr, function f, mixed extra, ...);
filter_array() returns an array holding the items of <arr> which passed
sucessfully through the function <fun> found in object <ob>. The func‐
tion <fun> is called for each element in <arr> with that element as
parameter. The second parameter <extra> and following parameters are
sent in each call if given. An object is considered to have passed
sucessfully through <fun> (and hence is included in the return array)
if <fun> returns 1. If f is passed it is used instead of ob->fun().
If <arr> is not an array, then 0 will be returned.