@Test
public void testCollectors() {
ArrayList<Person> people = new ArrayList<>();
ArrayList<Integer> things = new ArrayList<>();
ArrayList<Employee> employees = new ArrayList<>();
ArrayList<Student> students = new ArrayList<>();
// Accumulate names into a List
List<String> list = people.stream().map(Person::getName).collect(Collectors.toList());
// Accumulate names into a TreeSet
Set<String> list2 =
people.stream().map(Person::getName).collect(Collectors.toCollection(TreeSet::new));
// Convert elements to strings and concatenate them, separated by commas
String joined = things.stream().map(Object::toString).collect(Collectors.joining(", "));
// Find highest-paid employee
Optional<Employee> highestPaid =
employees.stream().collect(Collectors.maxBy(Comparator.comparingInt(Employee::getSalary)));
// Group employees by department
Map<Department, List<Employee>> byDept =
employees.stream().collect(Collectors.groupingBy(Employee::getDepartment));
// Find highest-paid employee by department
Map<Department, Optional<Employee>> highestPaidByDept =
employees
.stream()
.collect(
Collectors.groupingBy(
Employee::getDepartment,
Collectors.maxBy(Comparator.comparingInt(Employee::getSalary))));
// Partition students into passing and failing
Map<Boolean, List<Student>> passingFailing =
students.stream().collect(Collectors.partitioningBy(s -> s.getGrade() >= PASS_THRESHOLD));
}
/**
* Returns a vector of the maximum value of each column in the data frame
*
* @return a vector of the maximum value of each column in the data frame
*/
default Vector max() {
return collect(
Object.class,
org.briljantframework.data.Collectors.withFinisher(
Collectors.maxBy(ObjectComparator.getInstance()), Optional::get));
}