Lambda for nested for loop

Question

How would I apply grouping by collectors to fill up hashmaps for the following nested loops?

GroupingBy

Map schoolsByShortName = new HashMap();
Map schoolsByChair = new HashMap();

for(School school: List.getSchools()){
    if(school.getChairs()!= null){
        for(Chair chair: school.getChairs()){
            if(chair.getPrimaryChair()){
                List<School> schools = this.schoolsByChair.get(chair.getInitials());
                if(schools == null){
                    schools = new ArrayList<>();
                    this.schoolsByChair.put(chair.getInitials(), schools);
                }
                schools.add(school);
            }
        }
    }
    if(school.getShortName()!=null){
        this.schoolsByShortName.put(school.getShortName(), school);
    }
}

What have you got so far for your lambda version? Show us your attempt so we can see where you're stuck. — John Kugelman, Oct 02 '19 at 18:43
I got nothing so far, i'm starting new on lamdas and streams, was curious how this would look — dilbert2219, Oct 02 '19 at 18:47
Give it a try. We can help you when you get stuck but you should give it a go yourself first. — John Kugelman, Oct 02 '19 at 18:49
Aside: [Don't use raw types.](https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it) — Naman, Oct 03 '19 at 01:32

Reger05 · Accepted Answer · 2019-10-03T18:07:25.393

Something along the lines of this. Map stores as a set as I imagine each school entry should be unique. You can utilize a different Collection as needed.

        Function<School, String> getSchoolsPrimaryChairInitials = school -> school.getChairs()
                .stream()
                .filter(Chair::isPrimaryChair)
                .findFirst()
                .get()//consider possibility of not having primary chair
                .getInitials();

        Map<String, Set<School>> schoolsByChair = schools
                .stream()
                .collect(Collectors.groupingBy(getSchoolsPrimaryChairInitials, Collectors.toSet()));

        Map<String, Set<School>> schoolsByShortName = schools
                .stream()
                .collect(Collectors.groupingBy(School::getShortName, Collectors.toSet()));

Lambda for nested for loop

1 Answers1