table like java data structure

Question

hi. I need to implement some kind table-like data structure that stores info like this in Java:

+--------+-------+-----+
|  sij   |   i   |  j  |
+--------+-------+-----+
|   45   |   5   |  7  |
+--------+-------+-----+ 
|   33   |   1   |  6  |
+--------+-------+-----+ 
|   31   |   0   |  9  |
+--------+-------+-----+ 
|   12   |   8   |  2  |
+--------+-------+-----+

and i have to be able to sort the table by the sij parameter. I've made some tests with ArrayList and HashMap, but I can't make them work well.

hope you can help me!

thanks

Answer 1

What do you mean with:

i have to be able to sort it by the sij parameter

What's wrong with:

Object [][] data

EDIT

Ok, just guessing that what you need is a "StrangeDataStructure" which holds the array, and helps you to sort by the first column, then the only thing that you need is something like this:

class Structure {
    Object [][] data;
    Object [] indexColumn; // the sij?
}

And that's it: you should add a sort method indicating the direction, and sort using the "indexColumn"

It is VEEERY simple I think ( and If I understood your "question" )

You know what? I'm going to implement it.

// time elapses...

Here it is:

import java.util.Comparator;
import java.util.Arrays;

public class StrangeStructure {

    private Integer [][] data;
    private Integer [] sij; // what is sij anyway?

    public StrangeStructure( Integer [][] matrix  ) {
        data = matrix;
        sij = new Integer[ data.length ];
        for( int i = 0 ; i < data.length ; i++ ) {
            sij[i] = data[i][0];
        }
    }

    public void sort( Direction direction  ) {

        Comparator sijComparator  = new DataComparator( direction, true );
        Comparator dataComparator = new DataComparator( direction, false );

        Arrays.sort( sij, sijComparator );
        Arrays.sort( data, dataComparator  );

    }

    public static void main( String [] args ) {

        StrangeStructure s =  
            new StrangeStructure( new Integer[][]{
                                  { 45, 5, 7 }, 
                                  { 33, 1, 6 }, 
                                  { 31, 0, 9 }, 
                                  { 12, 8, 2 }    
                            });

        System.out.printf("Original:\n%s", s );       

        s.sort( Direction.MIN_TO_MAX );  
        System.out.printf("Min to max:\n%s", s );       

        s.sort( Direction.MAX_TO_MIN );  
        System.out.printf("Max to min\n%s", s );       

    }


    public String toString() {
        StringBuilder b = new StringBuilder();
        for( Integer [] row : data ) {
            for( int i : row ) {
                b.append( i+",");
            }
            b.append("\n");
        }
        return b.toString();

    }

}
class DataComparator implements Comparator {

    private Direction direction;
    private boolean isSij;

    public DataComparator( Direction d, boolean isSij ) {
        this.direction = d;
        this.isSij = isSij;
    }

    public int compare( Object one , Object two  ) {
        if( isSij ){
            return doCompare( direction, (Integer) one, (Integer) two );
        } else {
            return doCompare( direction, ((Integer[])one)[0], ((Integer[])two)[0]);
        }
    }
    public int doCompare( Direction d, int one, int two  ) {
        int a = ( d == Direction.MIN_TO_MAX? one: two );
        int b = ( d == Direction.MIN_TO_MAX? two: one ) ;
        return a - b;
    }
    public boolean equals( Object o ) {
        return false;
    }
}



enum Direction{
    MIN_TO_MAX,
    MAX_TO_MIN
}

Output:

Original:
45,5,7,
33,1,6,
31,0,9,
12,8,2,
Min to max:
12,8,2,
31,0,9,
33,1,6,
45,5,7,
Max to min
45,5,7,
33,1,6,
31,0,9,
12,8,2,

Answer 2

Read the section from the Swing tutorial on How to Use Tables. The tutorial shows how to create a table as well as how to add sorting capability to the table.

If you only need to store the data but not display it, then you can use a 2-dimensional array or a List of Lists. Then you can use the Column Comparator to do the sorting.

Edit: added code demonstrating use of the ColumnComparator

import java.util.*;

public class SortSIJ
{
    public static void main(String args[])
    {
        Object[] data = new Object[4];
     data[0] = new Integer[] {45, 5, 7};
     data[1] = new Integer[] {33, 1, 6};
     data[2] = new Integer[] {31, 0, 9};
     data[3] = new Integer[] {12, 8, 2};

     ColumnComparator cc = new ColumnComparator(0);
//   cc.setAscending( false );

     Arrays.sort(data, cc);

     for (Object row: data)
     {
      Integer[] theRow = (Integer[])row;
      System.out.println( Arrays.asList(theRow) );
     }
    }
}

I also agree with the suggestion to create an Object to store the 3 variables. In this case you can use the BeanComparator which can be found at the above link.

Answer 3

One option is to create a new object that contains the 3 variables, and then make an array/tree of those objects, and sort by the parameter you want.

Answer 4

Here's one way: make an object called Row to hold each row, and then make a java.util.HashMap whose keys are Integer sij's and whose values are the corresponding Rows.

public class Example
{
  public static class Row
  {
    public Integer sij;
    public Integer i;
    public Integer j;
    public Row(Integer sij, Integer i, Integer j)
    {
      this.sij = sij;
      this.i = i;
      this.j = j;
    }
  }

  public static void main(String[] args)
  {
    Row r1 = new Row(45, 5, 7);
    Row r2 = new Row(33, 1, 6);
    Row r3 = new Row(31, 0, 9);
    Row r4 = new Row(12, 8, 2);
    Map<Integer, Row> map = new TreeMap<Integer, Row>();
    map.put(r1.sij, r1);
    map.put(r2.sij, r2);
    map.put(r3.sij, r3);
    map.put(r4.sij, r4);
    for ( Row row : map.values() ) {
        System.out.println("sij: " + row.sij + " i: " + row.i + " j: " + row.j);
    }
  }
}

When this runs it produces:

sij: 12 i: 8 j: 2
sij: 31 i: 0 j: 9
sij: 33 i: 1 j: 6
sij: 45 i: 5 j: 7

Answer 5

You could use the MultiValueMap from Apache in order to link multiple values with one key.

Answer 6

If I understand your question right, all you need is a Comparable class to represent a row.

public static class Row
implements Comparable<Row> {
  public Row(int sij, int i, int j) {
    this.sij = sij;
    this.i = i;
    this.j = j;
  }

  public int compareTo(Row other) {
    return Integer.valueOf(sij).compareTo(other.sij);
  }

  public final int sij;
  public final int i;
  public final int j;
}

You can then populate a List with instances of Row and use Collections.sort to sort it.

Answer 7

HI, i want to thank all people here eho helpme! your comments were very userful