Multiple sort in java

Question

ArrayList data example: BJM 300 AC4507 TOM_JONES, BDM 290 DC4058 ALAN_FIELD, ADG 350 BA3240 JON_THORN

I need to sort the arraylist above into ascending sequence of the third column within the second column within the first column?

I tried nesting the loops as follows but it's not working! What am I doing wrong??

    public static ArrayList sortLoad1(ArrayList<TeachingLoad> loads){
    String s1, s2;
    TeachingLoad temp;                                   //Some local variables
    for(int i = 0 ; i < loads.size(); i++){              //Loop throuth 
        for(int j = loads.size()-1; j>i  ;j--){          //Loop through 
            s1 = loads.get(j-1).getSchoolCode();        //Extract 1st
            s2 = loads.get(j).getSchoolCode();          //Extract 2nd
                if(i+1<loads.size()&&s1.compareTo(s2)>-1){  //Compare them lexicographically
                    temp = loads.get(j-1);
                    //If s1 follows s2 then switch both
                    loads.set(j-1, loads.get(j));
                    loads.set(j, temp);
                }
                else{
                    for(int k = 0 ; k < loads.size(); k++){            
                        for(int l = loads.size()-1; l>i  ;l--){     
                            s1 = loads.get(l-1).getDepartmentNumber();
                            s2 = loads.get(l).getDepartmentNumber();
                            if(k+1<loads.size()&&s1.compareTo(s2)>-1){
                                temp = loads.get(l-1);
                                loads.set(l-1, loads.get(l));
                                loads.set(l, temp);
                            }
                            else{
                                for(int m = 0 ; m < loads.size(); m++){         
                                    for(int n = loads.size()-1; n>i  ;n--){         
                                        s1 = loads.get(n-1).getLecturerID();
                                        s2 = loads.get(n).getLecturerID();
                                        if(m+1<loads.size()&&s1.compareTo(s2)>-1){
                                            temp = loads.get(n-1);
                                            loads.set(n-1, loads.get(n));
                                            loads.set(n, temp);
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
        }//end loop
    }//end loop
    return loads;
}

I know I can use a Comparator to do this, but I don't want to.

Any help welcome?

Many thanks TeachingLoad held in arraylist is:

    public TeachingLoad(String schoolCode, String departmentNumber, 
        String lecturerID, String lecturerName, 
        String moduleNo, String creditHours, String classSize) {
    this.schoolCode = schoolCode;
    this.departmentNumber = departmentNumber;
    this.lecturerID = lecturerID;
    this.lecturerName = lecturerName;
    this.moduleNo = moduleNo;
    this.creditHours = creditHours;
    this.classSize = classSize;
}

public String getSchoolCode() {
    return schoolCode;
}

public String getDepartmentNumber(){
    return departmentNumber;
}

public String getModuleNo() {
    return moduleNo;
}

public String getCreditHours() {
    return creditHours;
}

public String getClassSize() {
    return classSize;
}
public String getLecturerID() {
    return lecturerID;
}

public String getLecturerName() {
    return lecturerName;
}

public void setLecturerID(String lecturerID) {
    this.lecturerID = lecturerID;
}

public void setLecturerName(String lecturerName) {
    this.lecturerName = lecturerName;
}

public void setSchoolCode(String schoolCode) {
    this.schoolCode = schoolCode;
}

public void setDepartmentNumber(String departmentNumber){
    this.departmentNumber = departmentNumber;
}

public void setModuleNo(String moduleNo) {
    this.moduleNo = moduleNo;
}

public void setCreditHours(String creditHours) {
    this.creditHours = creditHours;
}

public void setClassSize(String classSize) {
    this.classSize = classSize;
}

ETC

Cheers

can you add some quotes around that arraylist data, so we can see what you really have in there? (we're just humans, we can't tell whether you're delimited on spaces, or commas, or both, or...) — Mike 'Pomax' Kamermans
– Mike 'Pomax' Kamermans, Commented Dec 9, 2013 at 23:47
Are you sure you mean "third column within the second column within the third column"? You've got third column appearing twice, but your code uses three different keys. You'd probably find it easier if you either used Comparator with one of Java's sort methods, or if you have to implement your own sort, use one that works with a comparator function, so you separate out the sort logic from the key logic. — John Bickers
– John Bickers, Commented Dec 10, 2013 at 0:00

Stephen C · Accepted Answer · 2013-12-10 11:38:38Z

3

A sort algorithm should not have 6 levels of nested loop. I don't think this particular attempt can be "rescued".

My advice would be to start again:

Implement a simple Bubblesort algorithm. Alternatively use the Collections.sort method provided by the Java SE libraries. (Read the javadocs ... even if you don't plan to use it not ... because it is a good thing to know about it!!)
Implement and use the Comparator or Comparable interfaces, or your own custom "compare two TeachingLoad objects" method.

Note that there should only be two levels of nesting in a Bubblesort, which looks to be the algorithm that you were trying to implement.

While I agree with @Ingo that Bubblesort is a poor algorithm, I think that this is entirely beside the point. If you have been asked to implement a sort as a programming exercise, and you have not been taught about advanced sorting algorithms, then trying to implement an advanced algorithm is "jumping the gun". By all means learn about it, but if you try something too far in advance of your current skills you are setting yourself up to fail.

Or to put it another way, don't "show off" :-)

On the other hand, if:

you should know (say) Quicksort, and
you are expected to implement the algorithm from scratch,

then my advice would be different.

edited Dec 10, 2013 at 11:38

answered Dec 10, 2013 at 0:00

Stephen C

723k95 gold badges849 silver badges1.3k bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Ingo Over a year ago

And, unless you're a genius, use the sort function provided by your language/library. Bubblesort is just telling: "An idiot was here."

Stephen C Over a year ago

@Ingo - Maybe. We don't know if the OP is required to implement the sorting himself. This certainly seems like a "learning exercise".

TripVoltage Over a year ago

As I said I know I can use a comparator and yes I'm trying to do the sorting myself and was hoping for some pointers!

Ingo Over a year ago

Yes, maybe, but he didn't mention it. I'd also say that a prof who lets his studenst do bubblesort is .... well, at most semi-good.

Ingo Over a year ago

@TripVoltage - I acknowledge your striving for that. Two pointers: a) the base for a sorting algorithm is the comparision function and b) look for mergesort or quicksort, they are easy and good sorting algorithms. But first write a method that takes two data items and compares them.

Elliott Frisch · Accepted Answer · 2013-12-10 00:05:53Z

I don't understand what you hope to achieve with your approach; just use a Comparator like this

public static class TeachingLoadComparator implements Comparator<TeachingLoad> {

  /**
   * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
   */
  @Override
  public int compare(TeachingLoad o1, TeachingLoad o2) {
    if (o1 == null) {
      if (o2 == null) {
        return 0;
      }
      return -1;
    } else if (o2 == null) {
      return 1;
    }
    if (o1 == o2) {
      return 0;
    }
    switch (o1.getSchoolCode().compareTo(o2.getSchoolCode())) {
    case -1:
      return -1;
    case 1:
      return 1;
    }
    switch (o1.getDepartmentNumber().compareTo(o2.getDepartmentNumber())) {
    case -1:
      return -1;
    case 1:
      return 1;
    }
    return o1.getLecturerID().compareTo(o2.getLecturerID());
  }

and then use it with

Collections.sort(loads, new TeachingLoadComparator());

Community · Accepted Answer · 2017-05-23 11:57:32Z

1

Taking your input data, this is what I would do:

public class StringArraySort {

public static void main(String[] args) {

    List<String> arrayToSort = new ArrayList<String>();
    arrayToSort.add("BJM 300 AC4507 TOM_JONES"); 
    arrayToSort.add("BDM 290 DC4058 ALAN_FIELD"); 
    arrayToSort.add("ADG 350 BA3240 JON_THORN");
    arrayToSort.add("ADG 340 BA3240 JON_THORN");
    arrayToSort.add("ADF 340 BA3240 JON_THORN");

    Collections.sort(arrayToSort, customStringComparator);

    System.out.println(arrayToSort);

}

static final Comparator<String> customStringComparator = new Comparator<String>() {

    @Override
    public int compare(String o1, String o2) {
        String[] o1Columns = o1.split(" ");
        String[] o2Columns = o2.split(" ");

        if(o1Columns[2].compareTo(o2Columns[2]) == 0) {
            if(o1Columns[1].compareTo(o2Columns[1]) == 0) {
                // should it be first column?
                return o1Columns[0].compareTo(o2Columns[0]);
            } else {
                return o1Columns[1].compareTo(o2Columns[1]);
            }
        } else {
            return o1Columns[2].compareTo(o2Columns[2]);
        }
    }
}; }

I'm not sure I understood this statement:

third column within the second column within the third column?

So the columns may not be right.

As a rule of thumb always use a language construct, when there is one, in this case the Comparator.

EDIT: Seeing @Elliott Frisch's answer I think the best thing for you is to implement Comparable in your object.

2nd EDIT:

Here it is a method to do a simple bubble sort, but it is NOT advised for production code, as it performs very bad with large collections. Collections.sort(List list) is way faster, and if you look at the source you would see why.

public static <T extends Comparable<T>> void bubleSort(List<T> list) {
    boolean resort = false;
    for (int i = 0; i < list.size(); i++) {
        T t = list.get(i);
        int nextElementIndex = i + 1;
        if(nextElementIndex < list.size()) {
            T temp = list.get(nextElementIndex);
            if(t.compareTo(temp) > 0) {
                resort = true;
                list.set(nextElementIndex, t);
                list.set(i, temp);
            } else {
                continue;
            }
        } 
    }
    if(resort) {
        bubleSort(list);
    }
}

And here is the compareTo method from TeachingLoad:

public int compareTo(TeachingLoad o) {
        if(schoolCode.compareTo(o.schoolCode) == 0) {
            if(departmentNumber.compareTo(o.departmentNumber) == 0) {
                return lecturerID.compareTo(o.lecturerID);          
            }else {
                return departmentNumber.compareTo(o.departmentNumber);          
            }
        } else {
            return schoolCode.compareTo(o.schoolCode);
        }
    }

It's worth to mention that after a short Google search I found better algorithms than mine, like this, so I'm still not sure if this is what you are looking for.

edited May 23, 2017 at 11:57

CommunityBot

11 silver badge

answered Dec 10, 2013 at 0:22

Alberto de Paola

1,1602 gold badges15 silver badges29 bronze badges

6 Comments

TripVoltage Over a year ago

@ Alberto, it should have read sort the third within the second within the first - Thanks

Alberto de Paola Over a year ago

@TripVoltage You are welcome. Now I re read your question and some comments you made, and see that this wasn't what you were looking for. Are you allowed to see the java source code?

TripVoltage Over a year ago

@ Alberto - yes. I wanted to be able to do the sorting without using a comparator...

Alberto de Paola Over a year ago

@TripVoltage I'll try that in a few moments, it's interesting.

TripVoltage Over a year ago

@ Alberto - yeah it is.. suppose we count the number of ranges within a each field first then use these for the loop counter etc...

|

Collectives™ on Stack Overflow

Multiple sort in java

3 Answers 3

5 Comments

Comments

2nd EDIT:

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

5 Comments

Comments

2nd EDIT:

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related