just for who's interested,
i found a bit more simple way, at least in logic, for my specific 'problem':
using s2l in such a way that it breaks up the input into single characters,
then with [select -] filtering out this unwanted character. (see patch)
no leading zero's to worry about.

thanks Mathieu for your pointing out of GridFlow.
by the way, a search for gridflow on the Pd-site, returns with a number of broken links.
i gad to google for it.

rolf

#N canvas 392 162 569 343 10;
#X msg 51 -29 symbol 00-11-ab-7d-85-04;
#X text 206 -18 --example of the expected input;
#X msg 114 24 symbol;
#X obj 114 -2 loadbang;
#X obj 51 108 select -;
#X obj 165 122 t l;
#X obj 75 181 list;
#X obj 75 227 list2symbol;
#X obj 96 148 list prepend;
#X msg 138 201 symbol;
#X obj 138 175 loadbang;
#X obj 19 143 r end_drip;
#X text 182 200 -- get rid of the blanks;
#X obj 75 262 print b;
#X obj 51 76 list-drip;
#X obj 116 99 s end_drip;
#X obj 51 45 symbol2list;
#X text 154 25 --causes s2l to break the symbol into single characters
;
#X connect 0 0 16 0;
#X connect 2 0 16 1;
#X connect 3 0 2 0;
#X connect 4 1 8 0;
#X connect 5 0 8 1;
#X connect 6 0 7 0;
#X connect 7 0 13 0;
#X connect 8 0 5 0;
#X connect 8 0 6 1;
#X connect 9 0 7 1;
#X connect 10 0 9 0;
#X connect 11 0 6 0;
#X connect 14 0 4 0;
#X connect 14 1 15 0;
#X connect 16 0 14 0;