I would like to implement a group by feature in my program, this without having to export my array content in a file and process it in a database in order run a group by

Another way to avoid the file copying/-naming/-reading , and still enjoy full SQL power, is to copy your csv/tsv data into the clipboard (either via xclip of even simply Ctrl-A/C) and have a perl program sniff that clipboard-data, and read out the (clipboarded) csv data into a (perhaps temporary or foreign) table in a database (first generating a CREATE TABLE from the header line). This works well generically, even for pretty large data chunks, and takes almost no time.