: -rot rot rot ; [] '__A set : dip swap __A swap 1 compress append '__A
set execute __A -1 extract nip ; : nip swap drop ; : sum '+ reduce ;
: 2array 2 compress ; : comb "" split ; : lensize length nip ;
: <group> #( a -- 'a )
    grade subscript dup 's dress distinct strip
    length 1 2array reshape swap
    'A set
    : `filter(*)  A in A swap select ;
    '`filter apply
    ;

: elements(*)  lensize ;
: entropy #( s -- n )
    length "<group> 'elements apply" dip /
    dup neg swap log * 2 log / sum ;

"1223334444" comb entropy . # 1.84643934467102