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

DESCRIPTION
        ob->func() is called resp. cl applied to every element in the
        mapping, with first argument being the key of the
        element, and then the extra args that were given to
        filter_indices (these args must not be protected references like
        &(i[0]). If the function returns true, the element is
        added to the result mapping. ob can also be an object_name of an
        object.

        If <ob> is omitted, or neither a string nor an object, it
        defaults to this_object().

HISTORY
        In LDMud 3.2.6 renamed from filter_mapping() and generalised
        by efun filter().

SEE ALSO
        filter(E), map(E), map_indices(E), walk_mapping(E), member(E),
        m_contains(E)