Question

Basically, I have data of several people contained in a .csv file. This spreadsheet file contains the name of people in one column, followed by their age and work experience in two other columns.

So far I have correctly managed to display the data in a text area. However, I wish to be able to organise the people alphabetically by their name, or by their age in ascending order when the user clicks one of two buttons. For this example, I have attempted to limit the complexity by just trying to sort by age.

I have been told in order to do this, I should use a selection sort algorithm. Unfortunately, I have only used selection sort with arrays, not arrayLists, and not with data stored in a .csv file.

The problem that I have encountered is that I do not how to go through the data (for arrayLists), and then reassign the minimum position to the lowest number. Please refer to the minimumPosition method.

 public class Inputs extends JFrame
 {
   ArrayList <People> pList = new ArrayList <People>();
   JButton   NameSortButton;
   JTextArea DisplayTextArea; 

String outputText = "";

public Inputs()
{
        // Construct the GUI
      class innerListener implements ActionListener
    {
        public void actionPerformed (ActionEvent myActionEvent)
        {
            if (myActionEvent.getSource() == AgeSortButton)
            {
                sortByAge();
            }
        }
    }

    ActionListener inListener = new innerListener();
    NameSortButton.addActionListener(inListener);
}



public void readPeopleData()
{
    FileReader reader = null;
    int lineNumber = 1;

    try
    {
        reader = new FileReader("People.csv");
        Scanner in = new Scanner(reader);

        while (in.hasNextLine())
        {
            String input = in.nextLine();
            String section[] = input.split(",");
            pList.add(new People(section[0], section[1], Integer.parseInt(section[2]), Integer.parseInt(section[3])));
            lineNumber++;
        }

        for (People p: pList)
        {
            String heading = "Name \tAge \tWork Experience";
            outputText     = outputText + p.getPersonName()  +
                                  "\t"  + p.getAge()         +
                                  "\t"  + p.getExperience();
            DisplayTextArea.setText(heading + outputText);
        }
    }

    catch(IOException error)
    {
        JOptionPane.showMessageDialog(null, "File not Found","Error" , JOptionPane.ERROR_MESSAGE );
    }
} //    public void readPatientData()

private void sortByAge()
{
    for (int i = 0; i < pList.size(); i++)
    {
        int minPos = minimumPosition(i);
        swap(minPos, i);
    }
    displayOutputs();

}

private int minimumPosition(int from)
{
    int minPos = from;

    for (int i = from + 1; i < pList.size(); i++)
    {
                        // ****** PROBLEM AREA ****** //
        // if (pList.get(i).getAge() < // NO IDEA)
                          {
               minPos = i;
           }

                       /* 
                       The text book sorted arrays by: 
                       for (int i = from + 1; i < array.length; i ++)
                             if (array[i] < array[minPos])
                              {
                                   minPos = i;
                              } 
                       */

    }
    return minPos;
}


private void swap(int i, int j)
{
    People temp = pList.get(i);
    pList.set(i, pList.get(j));
    pList.set(j, temp);
}

private void displayOutputs ()
{
    for(int j = 0; j < pList.size(); j++)
    {
         outputText = outputText    + pList.get(j).getPersonName()     +
                               "\t" + pList.get(j).getAge()         +
                               "\t" + pList.get(j).getExperience()  +

        DisplayTextArea.setText(outputText);
        System.out.println(outputText);
    }
}

public static void main (String args[])
{
} //    public static void main (String args[])

}

Can somebody please point me in the right direction? How can I compare the sorted data to the unsorted data. Furthermore, are my for loops correct?

Thank you in advance.

Answer 1

Basically you could treat ArrayList like an array, since it is a list backed by an array.

You’re already on a good way with you implementation.

Instead of this:

for (int i = from + 1; i < array.length; i ++) {
  if (array[i] < array[minPos]) {
    minPos = i;
  } 
}

You’d replace the array access with list operations:

for (int i = from + 1; i < pList.size(); i ++) {
  if ( pList.get(i).getAge() < pList.get(minPos ).getAge() ) {
    minPos = i;
  } 
}