Creating files based on column from 2D Matrix - Java -

i have big matrix nx2 - yes 2 columns thousand of lines) , create 1 file per "group" of lines. grouping should done columns has date.

my matrix sorted, i'm struggling create file in have each line representing record former matrix

for example, have following structure in matrix:

 col0  col1  1234   environmental sciences & ecology  1997   chemistry; mathematics; physics  1997   science & technology - other topics  1997   neurosciences & neurology; physiology  2002   dermatology  2005   biochemistry & molecular biology  2005   geochemistry & geophysics 

each "date" (they string in code) file respecting value(s). in case, 1997 , 2005 2 lines each, 1 each "repetition".

my question is, how put every record (in separate lines) each date. ordered in attempt make things easier didn't help

any welcome.

you can use map<string, list<string>> collecting data in groups year. can iterate through map , create file each entry , write entry values map.