In truth, this should not be done in SQL. Unless the pairing of aaa, ddd, and ggg has some meaning then this is client-side formatting and shouldn't be done on the server.
EDIT:
In the interests if an intellectual exercise, something like this seems to work.
select
f1.data, f2.data, f3. data
from (select data, ROW_NUMBER() over (order by data) as row_num from your_table) f1
left join (select data, ROW_NUMBER() over (order by data) as row_num from your_table) f2 on f2.row_num = f1.row_num + (select CEILING(COUNT(1) / 3) + 1 from your_table)
left join (select data, ROW_NUMBER() over (order by data) as row_num from your_table) f3 on f3.row_num = f1.row_num + (select CEILING(COUNT(1) / 3) + 1 from your_table) * 2
where f1.row_num between 1 and FLOOR((select COUNT(1) from your_table) / 3) + 1
But, again, I suspect that this is really something that should be done client-side, NOT in SQL.