Filter Java 8 list to contain elements based on thresholds defined in other list - java-8

Question

I have a sample program below where subject passing marks thresholds are defined in Metadata. The studentMarks list should be filtered in a way so that the resulting list will contain all the subjects of a student where the marks scored are greater than the threshold in at least one subject.
import lombok.Builder;
import lombok.Getter;
import java.util.ArrayList;
import java.util.List;
public class TestClass {
public static void main(String[] args) {
TestClass test = new TestClass();
List<Metadata> metadataList = test.buildMetadata();
List<StudentMarks> studentMarks = test.buildStudentMarks();
// filter studentMarks list so that the resulting list will contain
// all records (subjects) of first and second students because
// they scored above the threshold in at least one of the subjects
}
private List<StudentMarks> buildStudentMarks() {
List<StudentMarks> studentMarks = new ArrayList<>();
StudentMarks firstStudMath = StudentMarks.builder().subject("MATH").marks(93).build();
StudentMarks firstStudEng = StudentMarks.builder().subject("ENG").marks(45).build();
StudentMarks firstStudPE = StudentMarks.builder().subject("PE").marks(80).build();
StudentMarks secondStudMath = StudentMarks.builder().subject("MATH").marks(74).build();
StudentMarks secondStudEng = StudentMarks.builder().subject("ENG").marks(59).build();
StudentMarks secondStudPE = StudentMarks.builder().subject("PE").marks(88).build();
StudentMarks thirdStudMath = StudentMarks.builder().subject("MATH").marks(50).build();
StudentMarks thirdStudEng = StudentMarks.builder().subject("ENG").marks(50).build();
StudentMarks thirdStudPE = StudentMarks.builder().subject("PE").marks(50).build();
studentMarks.add(firstStudMath);
studentMarks.add(firstStudEng);
studentMarks.add(firstStudPE);
studentMarks.add(secondStudMath);
studentMarks.add(secondStudEng);
studentMarks.add(secondStudPE);
studentMarks.add(thirdStudMath);
studentMarks.add(thirdStudEng);
studentMarks.add(thirdStudPE);
return studentMarks;
}
private List<Metadata> buildMetadata() {
List<Metadata> metadataList = new ArrayList<>();
Metadata math = Metadata.builder().subject("MATH").marksThreshold(75).build();
Metadata english = Metadata.builder().subject("ENG").marksThreshold(60).build();
Metadata pe = Metadata.builder().subject("PE").marksThreshold(80).build();
// more subjects
metadataList.add(math);
metadataList.add(english);
metadataList.add(pe);
return metadataList;
}
}
#Getter #Builder
class StudentMarks {
private Integer rollNum; //unique identifier
private String subject;
private Integer marks;
}
#Getter #Builder
class Metadata {
private String subject;
private Integer marksThreshold;
}
Based on the thresholds (Metadata), the output list would contain all the records for firstStud and secondStud BECAUSE these students scored more than the threshold in AT LEAST one subject. In the example above, the output list will have 6 records (2 passed students * 3 subjects each student)
The Metadata can have more or less subjects depending on the use case and there can be any number of students in studentMarks list. However, each student will always have same number of records (subjects) as defined in Metadata.
Update:
This is how I implemented this. Please suggest if this can be further optimized or shortened.
import lombok.Builder;
import lombok.EqualsAndHashCode;
import lombok.Getter;
import lombok.ToString;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class TestClass {
public static void main(String[] args) {
TestClass test = new TestClass();
List<Metadata> metadataList = test.buildMetadata();
List<StudentMarks> studentMarks = test.buildStudentMarks();
// filter studentMarks list so that the resulting list will contain
// all records (subjects) of first and second students because
// they scored above the threshold in at least one of the subjects
Map<Integer, List<StudentMarks>> lookup =
studentMarks.stream().collect(Collectors.groupingBy(StudentMarks::getRollNum));
System.out.println(lookup);
// Output:
//{1=[StudentMarks(rollNum=1, subject=MATH, marks=93), StudentMarks(rollNum=1, subject=ENG, marks=45), StudentMarks(rollNum=1, subject=PE, marks=80)],
// 2=[StudentMarks(rollNum=2, subject=MATH, marks=74), StudentMarks(rollNum=2, subject=ENG, marks=59), StudentMarks(rollNum=2, subject=PE, marks=88)],
// 3=[StudentMarks(rollNum=3, subject=MATH, marks=50), StudentMarks(rollNum=3, subject=ENG, marks=50), StudentMarks(rollNum=3, subject=PE, marks=50)]}
lookup.forEach((k, v) -> {
boolean filter = true;
for (Metadata m : metadataList) {
StudentMarks sm = v.stream().filter(s -> s.getSubject().equalsIgnoreCase(m.getSubject())).findFirst().get();
if (m.getMarksThreshold() <= sm.getMarks()) {
filter = false;
break;
}
}
if (!filter) System.out.println(v);
});
}
private List<StudentMarks> buildStudentMarks() {
List<StudentMarks> studentMarks = new ArrayList<>();
StudentMarks firstStudMath = StudentMarks.builder().rollNum(1).subject("MATH").marks(93).build();
StudentMarks firstStudEng = StudentMarks.builder().rollNum(1).subject("ENG").marks(45).build();
StudentMarks firstStudPE = StudentMarks.builder().rollNum(1).subject("PE").marks(80).build();
StudentMarks secondStudMath = StudentMarks.builder().rollNum(2).subject("MATH").marks(74).build();
StudentMarks secondStudEng = StudentMarks.builder().rollNum(2).subject("ENG").marks(59).build();
StudentMarks secondStudPE = StudentMarks.builder().rollNum(2).subject("PE").marks(88).build();
StudentMarks thirdStudMath = StudentMarks.builder().rollNum(3).subject("MATH").marks(50).build();
StudentMarks thirdStudEng = StudentMarks.builder().rollNum(3).subject("ENG").marks(50).build();
StudentMarks thirdStudPE = StudentMarks.builder().rollNum(3).subject("PE").marks(50).build();
studentMarks.add(firstStudMath);
studentMarks.add(firstStudEng);
studentMarks.add(firstStudPE);
studentMarks.add(secondStudMath);
studentMarks.add(secondStudEng);
studentMarks.add(secondStudPE);
studentMarks.add(thirdStudMath);
studentMarks.add(thirdStudEng);
studentMarks.add(thirdStudPE);
return studentMarks;
}
private List<Metadata> buildMetadata() {
List<Metadata> metadataList = new ArrayList<>();
Metadata math = Metadata.builder().subject("MATH").marksThreshold(75).build();
Metadata english = Metadata.builder().subject("ENG").marksThreshold(60).build();
Metadata pe = Metadata.builder().subject("PE").marksThreshold(80).build();
// more subjects
metadataList.add(math);
metadataList.add(english);
metadataList.add(pe);
return metadataList;
}
}
#Getter #Builder #ToString
class StudentMarks {
private Integer rollNum;
private String subject;
private Integer marks;
}
#Getter #Builder #ToString #EqualsAndHashCode(onlyExplicitlyIncluded = true)
class Metadata {
#EqualsAndHashCode.Include
private String subject;
private Integer marksThreshold;
}

Answer 1

To achieve your target, there is one important thing required, which is a field in the StudentMarks class, to uniquely identify your student. I am assuming that field to be rollNum. On the basis of that, we can achieve the desired result as follows:
Create a map of the student and his/her marks. (rollNum -> List<StudentMarks>);
Iterate over the entries of the map, and for each entry check, whether the student has marks in any one subject greater than the threshold.
Here is the code, for that:
import lombok.Builder;
import lombok.Getter;
import java.util.*;
public class Sample {
public static void main(String[] args) {
Sample test = new Sample();
List<Metadata> metadataList = test.buildMetadata();
List<StudentMarks> studentMarks = test.buildStudentMarks();
Map<Integer, List<StudentMarks>> rollNoToMarksMap = new HashMap<>();
// Create a map of student rollNum to his list of marks
for(StudentMarks marks: studentMarks) {
if(rollNoToMarksMap.containsKey(marks.getRollNum())) {
rollNoToMarksMap.get(marks.getRollNum()).add(marks);
} else {
rollNoToMarksMap.put(marks.getRollNum(), new ArrayList<>(Arrays.asList(marks)));
}
}
studentMarks.clear();
// Loop over the map entries to see if the student has marks in any one subject greater than the threshold
for(Map.Entry<Integer, List<StudentMarks>> studentEntry : rollNoToMarksMap.entrySet()) {
List<StudentMarks> studentMark = studentEntry.getValue();
Boolean greaterThanThreshold =
studentMark.stream().anyMatch(
mark -> metadataList.stream()
.anyMatch(
metadata -> metadata.getSubject().equals(mark.getSubject()) && mark.getMarks() > metadata.getMarksThreshold()));
if(greaterThanThreshold) {
System.out.println("Roll Number " + studentEntry.getKey());
studentMarks.addAll(studentMark);
}
}
System.out.println("Total Entries in the list " + studentMarks.size());
}
private List<StudentMarks> buildStudentMarks() {
List<StudentMarks> studentMarks = new ArrayList<>();
StudentMarks firstStudMath = StudentMarks.builder().subject("MATH").marks(93).rollNum(1).build();
StudentMarks firstStudEng = StudentMarks.builder().subject("ENG").marks(45).rollNum(1).build();
StudentMarks firstStudPE = StudentMarks.builder().subject("PE").marks(80).rollNum(1).build();
StudentMarks secondStudMath = StudentMarks.builder().subject("MATH").marks(74).rollNum(2).build();
StudentMarks secondStudEng = StudentMarks.builder().subject("ENG").marks(59).rollNum(2).build();
StudentMarks secondStudPE = StudentMarks.builder().subject("PE").marks(88).rollNum(2).build();
StudentMarks thirdStudMath = StudentMarks.builder().subject("MATH").marks(50).rollNum(3).build();
StudentMarks thirdStudEng = StudentMarks.builder().subject("ENG").marks(50).rollNum(3).build();
StudentMarks thirdStudPE = StudentMarks.builder().subject("PE").marks(50).rollNum(3).build();
studentMarks.add(firstStudMath);
studentMarks.add(firstStudEng);
studentMarks.add(firstStudPE);
studentMarks.add(secondStudMath);
studentMarks.add(secondStudEng);
studentMarks.add(secondStudPE);
studentMarks.add(thirdStudMath);
studentMarks.add(thirdStudEng);
studentMarks.add(thirdStudPE);
return studentMarks;
}
private List<Metadata> buildMetadata() {
List<Metadata> metadataList = new ArrayList<>();
Metadata math = Metadata.builder().subject("MATH").marksThreshold(75).build();
Metadata english = Metadata.builder().subject("ENG").marksThreshold(60).build();
Metadata pe = Metadata.builder().subject("PE").marksThreshold(80).build();
// more subjects
metadataList.add(math);
metadataList.add(english);
metadataList.add(pe);
return metadataList;
}
}
#Getter #Builder
class StudentMarks {
Integer rollNum;
String subject;
Integer marks;
}
#Getter #Builder
class Metadata {
String subject;
Integer marksThreshold;
}