java - How can I iterate through a Date/Time column in a CSV file when the dates are different for each file -

so format of date/time column in csv file looks this:

csv[0]                      csv[1]       2014-06-02t00:00:00         somenumericaldata 2014-06-03t00:00:00         etc...  

depending on file i'm working with, 2013, 2012 etc. want able numerical data in other column each day of data. numerical data 2014-06-02 in 1 array/list, when hit next date, store data in new array/list.

i can iterate through csv , data fine, it's checking dates that's bugging me. if can or point me in right direction how tackle great. (note: data relevant, time doesn't matter)

one way use map grouping values same date. can use hashmap, or better use treemap entries sorted date.

i don't want bother reading csv input, i'll put example data map (those don't have ordered). adapting csv approach should trivial.

map<string, double> ungroupedcsv = new treemap<>(); ungroupedcsv.put("2014-06-02t00:01:00", 1.1); ungroupedcsv.put("2014-06-02t00:02:00", 1.2); ungroupedcsv.put("2014-06-02t03:00:00", 1.3); ungroupedcsv.put("2014-06-02t04:20:00", 1.4); ungroupedcsv.put("2014-06-03t00:00:01", 2.1); ungroupedcsv.put("2014-06-03t00:01:00", 2.2); ungroupedcsv.put("2014-06-03t00:11:00", 2.3); ungroupedcsv.put("2014-06-03t01:10:00", 2.4); 

next need 2 date formats: 1 original format, date , time, , 1 date only:

simpledateformat datetime = new simpledateformat("yyyy-mm-dd't'hh:mm:ss"); simpledateformat dateonly = new simpledateformat("yyyy-mm-dd"); 

the grouped dates stored in map, mapping date-only string in above format lists of numerical values original list.

map<string, list<double>> grouped = new treemap<>(); 

now can iterate entries in original map (or csv file), re-code date format, , add value respective date-list (or create list if not yet exist).

for (string key : ungroupedcsv.keyset()) {     string date = dateonly.format(datetime.parse(key));     if (! grouped.containskey(date)) {         grouped.put(date, new arraylist<double>());     }     grouped.get(date).add(ungroupedcsv.get(key)); } system.out.println(grouped); 

output:

{2014-06-02=[1.1, 1.2, 1.3, 1.4], 2014-06-03=[2.1, 2.2, 2.3, 2.4]}