Newbie trying to sort 2D string array

Question

Dear all,
After read some book chapters, web sites including this, I still don't get the point.
If I have a file like,
1 aaa 213 0.9
3 cbb 514 0.1
2 abc 219 1.3
9 bbc 417 10.4
8 dee 887 2.1
9 bba 111 7.1
and I load into memory as a String[][]
here comes the problem, I sort by column 1 (aaa,...,bba) using an adaptation of the Quicksort algorithm for 2D arrays
* Sort for a 2D String array
* @param a an String 2D array
* @param column column to be sort
public static void sort(String[][] a, int column) throws Exception {
QuickSort(a, 0, a.length - 1, column);
/** Sort elements using QuickSort algorithm
static void QuickSort(String[][] a, int lo0, int hi0, int column) throws Exception {
int lo = lo0;
int hi = hi0;
int mid;
String mitad;
if ( hi0 > lo0) {
/* Arbitrarily establishing partition element as the midpoint of
* the array.
mid = ( lo0 + hi0 ) / 2 ;
mitad = a[mid][column];
// loop through the array until indices cross
while( lo <= hi ) {
/* find the first element that is greater than or equal to
* the partition element starting from the left Index.
while( ( lo < hi0 ) && ( a[lo][column].compareTo(mitad)<0))
++lo;
/* find an element that is smaller than or equal to
* the partition element starting from the right Index.
while( ( hi > lo0 ) && ( a[hi][column].compareTo(mitad)>0))
--hi;
// if the indexes have not crossed, swap
if( lo <= hi )
swap(a, lo, hi);
++lo;
--hi;
/* If the right index has not reached the left side of array
* must now sort the left partition.
if( lo0 < hi )
QuickSort( a, lo0, hi, column );
/* If the left index has not reached the right side of array
* must now sort the right partition.
if( lo < hi0 )
QuickSort( a, lo, hi0, column );
* swap 2D String column
private static void swap(String[][] array, int k1, int k2){
String[] temp = array[k1];
array[k1] = array[k2];
array[k2] = temp;
----- end of the code --------
if I call this from the main module like this
import MyUtil.*;
public class kaka
public static void main(String[] args) throws Exception
String[][]a = MyUtil.fileToArray("array.txt");
MyMatrix.printf(a);
System.out.println("");
MyMatrix.sort(a,1);
MyMatrix.printf(a);
System.out.println("");
MyMatrix.sort(a,3);
MyMatrix.printf(a);
for the first sorting I get
1 aaa 213 0.9
2 abc 219 1.3
9 bba 111 7.1
9 bbc 417 10.4
3 cbb 514 0.1
8 dee 887 2.1
(lexicographic)
but for the second one (column 3) I get
3 cbb 514 0.1
1 aaa 213 0.9
2 abc 219 1.3
9 bbc 417 10.4
8 dee 887 2.1
9 bba 111 7.1
this is not the order I want to apply to this sorting, I would like to create my own one. but or I can't or I don't know how to use a comparator on this case.
I don't know if I am rediscovering the wheel with my (Sort String[][], but I think that has be an easy way to sort arrays of arrays better than this one.
I've been trying to understand the Question of the week 106 (http://developer.java.sun.com/developer/qow/archive/106/) that sounds similar, and perfect for my case. But I don't know how to pass my arrays values to the class Fred().
Any help will be deeply appreciated
Thanks for your help and your attention
Pedro

Answer 1

public class StringArrayComparator implements Comparator {
  int sortColumn = 0;
  public int setSortColumn(c) { sortColumn = c; }
  public int compareTo(Object o1, Object o2) {
    if (o1 == null && o2 == null)
      return 0;
    if (o1 == null)
      return -1;
    if (o2 == null)
      return 1;
    String[] s1 = (String[])o1;
    String[] s2 = (String[])o2;
    // I assume the elements at position sortColumn is
    // not null nor out of bounds.
    return s1[sortColumn].compareTo(s2[sortColumn]);
// Then you can use this to sort the 2D array:
Comparator comparator = new StringArrayComparator();
comparator.setSortColumn(0); // sort by first column
String[][] array = ...
Arrays.sort(array, comparator);I haven't tested the code, so there might be some compiler errors, or an error in the logic.