There's no built-in subtotaling feature in TT, but you could possibly put your data into a Data::Table
object, that would give you some ability to handle subtotaling at the 'meta' level, as you say.
Depending on the number of columns involved though, it might be just as simple to create local hashes to maintain running totals: NB: untested, example code only
[%-
MACRO printrow(rowtype, line) BLOCK;
# however you print the row as LaTeX
# rowtype is 'row', 'subtotal' or 'grandtotal' for formatting purposes
END;
SET sumcols = [ 'col3', 'col4', 'col5' ]; # cols to be accumulated
SET s_tot = {}; SET g_tot = {};
FOREACH i IN sumcols;
SET s_tot.$i = 0; # initialise
SET g_tot.$i = 0;
END;
FOREACH row IN data;
IF s_tot.col2 AND s_tot.col2 <> row.col2; # start of new group
printrow('subtotal', s_tot);
FOREACH i IN sumcols;
SET s_tot.$i = 0; #re-init
END;
END;
printrow('row', row);
SET s_tot.col2 = row.col2; # keep track of group level
FOREACH i IN sumcols;
SET s_tot.$i = s_tot.$i + row.$i;
SET g_tot.$i = g_tot.$i + row.$i;
END;
END;
printrow('grandtotal', g_tot);
-%]
Of course, if you have more than a couple of grouping levels, this can get quite messy. You could make s_tot
an array of hashes to manage each level, to avoid hard-coding the levels. That's left as an exercise for the reader, as they say.