arraylist - Java List, Counting non-zero attributes of Object, by group of 3 -

i have arraylist<fileline> , inside fileline function

public double getvalue() {     ...     doing stuff     ...     return value; } 

what i'm trying return count of non-zero getvalue() of group of 3 filelines.

let's have list<fileline> filelines of filelines.size() = 12 , respective getvalue() 0,0,0, 0,1,2, 0,3,0, 4,5,5 result i'd 3, valid expect first group.

if group of 1 fileline filter , count :

long resultcount = filelines.stream().filter(x -> x.getvalue() > 0).count(); 

, fact it's group of 3 causing me problem.

is best approach split list multiple 3 elements sublists or more elegant way?

you can group 3 mapping range of indices sublists this:

list<fileline> filtered = intstream.range(0, list.size()/3)     .maptoobj(n -> list.sublist(n*3, n*3+3))     .filter(sublist -> sublist.stream().anymatch(fl -> fl.getvalue() != 0.0))     .flatmap(list::stream)     .collect(collectors.tolist()); 

i assume want flatten groups back, added flatmap step. alternatively can leave them grouped if it's better in case:

list<list<fileline>> filtered = intstream.range(0, list.size()/3)     .maptoobj(n -> list.sublist(n*3, n*3+3))     .filter(sublist -> sublist.stream().anymatch(fl -> fl.getvalue() != 0.0))     .collect(collectors.tolist()); 

if need count such groups, replace collect step count , merge map , filter single step:

long count = intstream.range(0, list.size()/3)     .filter(n -> list.sublist(n*3, n*3+3).stream().anymatch(fl -> fl.getvalue() != 0.0))     .count();