SYNOPSIS
	mapping filter_mapping(mapping, string func, object ob, ...)
	mapping filter_mapping(mapping, closure cl, ...)

DESCRIPTION
	ob->func() is called resp. cl applied to every element in the
	mapping, with first argument the first data item of the
	element, and then the extra args that were given to
	map_mapping. If the function returns true, the element is
	added to the result mapping. ob can also be a file_name of an
	object. If the second arg is a string and the third is not an
	object, this_object() will be used as default.

SEE ALSO
	map_array(E), walk_mapping(E), member(E), mapping_contains(E)