How can i filter employee list based on the "City filter list" and maintain the filter order using java 8.

I want to filter Employee (list1) objects by city name based on the another list(filterList : referring City) and create new list(list2) and maintain hte filterList City order using Java 8.

Important Note : Here new list should be in same order where the filterList(City name) there.

Input :

List<Employee> list1 = Stream.of(
                        new Employee("100","Boston","Massachusetts"),
                        new Employee("400","Atlanta","Georgia"),
                        new Employee("300","pleasanton","California"),
                        new Employee("200","Decatur","Texas"),
                        new Employee("500","Cumming","Atlanta"),
                        new Employee("98","sula","Maine"),
                        new Employee("156","Duluth","Ohio"))
                .collect(Collectors.toList());

Filter List :

List<String> filterList = Stream.of("pleasanton", "Atlanta", "Cumming", "Boston").collect(Collectors.toList());

Expected output :

List<Employee> list2 = Stream.of(
                        new Employee("300","pleasanton","California"),
                        new Employee("400","Atlanta","Georgia"),
                        new Employee("500","Cumming","Atlanta"),
                        new Employee("100","Boston","Massachusetts"))
                .collect(Collectors.toList());

CodePudding user response：

Well this is a multi-step process. Firstly, I don't see any point in creating an intermediate stream, just for the sake of creating a Collection. There are more Collection library methods such as good old Arrays.asList which you would use to create a collection easily without creating unnecessary intermediate objects. Here's a linear time solution to your problem.

final List<String> filterList = Arrays.asList("pleasanton", "Atlanta", "Cumming", "Boston");

final Map<String, Integer> posMap = IntStream.range(0, filterList.size()).boxed()
        .collect(Collectors.toMap(filterList::get, i -> i));
final Set<String> cities = new HashSet<>(filterList);
final Collection<Employee> sortedEmps = list1.stream().filter(e -> cities.contains(e.getCity()))
    .sorted(Comparator.comparing(e -> posMap.get(e.getCity()))).collect(Collectors.toList()); 

Note that you sort the elements based on their position in the input array, and the use of a Set to check the containment brings otherwise quadratic time solution to a linear one.

CodePudding user response：

Try this:

import java.util.*;
import java.util.stream.*;
class Employee {
    private String salary;
    private String city;
    private String state;
    
    public Employee(String salary, String city, String state) {
        this.salary = salary;
        this.city = city;
        this.state = state;
    }
    
    public String getSalary() {
        return salary;
    }
    
    public String getCity() {
        return city;
    }
    
    public String getState() {
        return state;
    }
}

public class Main {
    public static void main(String[] args) {
        List<Employee> list1 = Stream.of(
                        new Employee("100","Boston","Massachusetts"),
                        new Employee("400","Atlanta","Georgia"),
                        new Employee("300","pleasanton","California"),
                        new Employee("200","Decatur","Texas"),
                        new Employee("500","Cumming","Atlanta"),
                        new Employee("98","sula","Maine"),
                        new Employee("156","Duluth","Ohio"))
                .collect(Collectors.toList());
        
        List<String> filterList = Stream.of("pleasanton", "Atlanta", "Cumming", "Boston").collect(Collectors.toList());
        
        List<Employee> list2 = list1.stream().filter(e -> filterList.contains(e.getCity())).sorted((a, b) -> filterList.indexOf(a.getCity()) - filterList.indexOf(b.getCity())).collect(Collectors.toList());
    list2.stream().forEach(e -> {
                System.out.println("City "   e.getCity());
                System.out.println("State "   e.getState());
                System.out.println("Salary "   e.getSalary());
                System.out.println();
        });
    }
}