Subtract the values for each group in java 8 - java-8

Question

I have class Data10 which have 5 fields and have list of values then i want to subtract the value from each unique id group of valuePeriod as below example then finally in result generate new Data10 object with same id, same year, new name, same valuePeriod and result of subtraction of the value.
Note: Below example I have only 2 name which i want to subtract from A-B then name become "C" in the expected result.
Important note: I want to do A-B not a B-A.
class Data10 {
int id;
int year;
String name;
int valuePeriod;
BigDecimal value;
}
List<Data10> list = new ArrayList();
list.add(new Data10(1, 2020, "A", 1, new BigDecimal(5.5)));
list.add(new Data10(1, 2020, "B", 1, new BigDecimal(2.5)));
list.add(new Data10(1, 2020, "A", 2, new BigDecimal(8.5)));
list.add(new Data10(1, 2020, "B", 2, new BigDecimal(1.5)));
list.add(new Data10(1, 2020, "A", 3, new BigDecimal(6.5)));
list.add(new Data10(1, 2020, "B", 3, new BigDecimal(2.5)));
list.add(new Data10(2, 2020, "A", 1, new BigDecimal(6.5)));
list.add(new Data10(2, 2020, "B", 1, new BigDecimal(1.5)));
list.add(new Data10(2, 2020, "A", 2, new BigDecimal(9.5)));
list.add(new Data10(2, 2020, "B", 2, new BigDecimal(3.5)));
list.add(new Data10(2, 2020, "A", 3, new BigDecimal(7.5)));
list.add(new Data10(2, 2020, "B", 3, new BigDecimal(5.5)));
I try with grouped the data but how to subtract value for same valuePeriod then generate new object? Any help please. Thanks in advance!
list.stream().collect(Collectors.groupingBy(Data10::getId, Collectors.groupingBy(Data10::getValuePeriod)));
Expected Result:
Data10(1, 2020, "C", 1, 3.0); (Subtract the value for same valuePeriod A-B)
Data10(1, 2020, "C", 2, 7.0);
Data10(1, 2020, "C", 3, 4.0);
Data10(2, 2020, "C", 1, 5.0);
Data10(2, 2020, "C", 2, 6.0);
Data10(2, 2020, "C", 3, 2.0);

Answer 1

If I can think of a better way I will post it. But for now it's a two stage process.
first create a map using the name, id, valuePeriod, and year as the key. This presumes every A has a matching B (else it gets more complicated).
Map<String, Data10> map =
list.stream()
.collect(Collectors.toMap(
d -> d.getName() + d.getId()
+ d.getValuePeriod()+d.getYear(),
d -> d));
map.entrySet().forEach(System.out::println);
prints
A112020=[1, 2020, A, 1, 5.5]
A222020=[2, 2020, A, 2, 9.5]
A232020=[2, 2020, A, 3, 7.5]
A122020=[1, 2020, A, 2, 8.5]
A132020=[1, 2020, A, 3, 6.5]
B212020=[2, 2020, B, 1, 1.5]
B222020=[2, 2020, B, 2, 3.5]
B112020=[1, 2020, B, 1, 2.5]
B232020=[2, 2020, B, 3, 5.5]
A212020=[2, 2020, A, 1, 6.5]
B132020=[1, 2020, B, 3, 2.5]
B122020=[1, 2020, B, 2, 1.5]
Now stream the original list and use the map to reference the appropriate key, filtering out the "B" values.
Create a new Data10 instance, populating the existing values along with the difference of A-B
List<Data10> result = list.stream().filter(d->d.getName().equals("A"))
.map(d->new Data10(d.getId(),
d.getYear(), "C", d.getValuePeriod(),
map.get("A" + d.getId() + d.getValuePeriod()+d.getYear()).getValue()
.subtract(map.get("B" + d.getId()
+ d.getValuePeriod()+d.getYear()).getValue())))
.toList();
result.forEach(System.out::println);
prints
[1, 2020, C, 1, 3.0]
[1, 2020, C, 2, 7.0]
[1, 2020, C, 3, 4.0]
[2, 2020, C, 1, 5.0]
[2, 2020, C, 2, 6.0]
[2, 2020, C, 3, 2.0]
I made an assumption that there could be different years that might have the same valuePeriod so it was necessary to include it in the key so as to target the appropriate values. You can of course modify to fit your exact requirements.