Sorting a vector where each element is a vector

Question

Hi,
Sorry for the post but I can't seem to get my head around sorting in Java using Comparator.
I've a vector where each element is a vector containing strings, integers and doubles and the first element of each vector is a double.
I need to sort the vector based on this first value of each element which is a vector.
Hope some can help,
Thanks in advance,
Lou

Answer 1

Here is a generic comparator you can use to sort a List. Vector implements the List interface to you can sort the Vector.
import java.util.Comparator;
import java.util.List;
* A comparator to sort Lists of data based on a column within each List
public class ListComparator implements Comparator
    private int column;
    private boolean ascending;
    ListComparator(int column, boolean ascending)
        this.column = column;
        this.ascending = ascending;
    public int compare(Object a, Object b)
        List v1 = (List)a;
        List v2 = (List)b;
        Object o1 = v1.get(column);
        Object o2 = v2.get(column);
        // Treat empty strings like nulls
        if (o1 instanceof String && ((String)o1).length() == 0)
            o1 = null;
        if (o2 instanceof String && ((String)o2).length() == 0)
            o2 = null;
        // Sort nulls so they appear last, regardless  of sort order
        if (o1 == null && o2 == null) return 0;
        if (o1 == null) return 1;
        if (o2 == null) return -1;
        //  Compare objects
        if (o1 instanceof Comparable)
            if (ascending)
                return ((Comparable)o1).compareTo(o2);
            else
                return ((Comparable)o2).compareTo(o1);
        else  // Compare as a String
            if (ascending)
                return o1.toString().compareTo(o2.toString());
            else
                 return o2.toString().compareTo(o1.toString());
}You invoke the sort by using:
Collections.sort(yourVector, new ListComparator(column, ascending));