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;