Sorting multiple lists by the values of another list in java

Question

I have 6 ArrayLists as shown below:

index: 0         1           2          3            4          5

[12345.12   |123.0      |12.12      |1234.0     |123.12     |123.12    ] <Double>
[2000-01-11 |2000-01-11 |2000-01-11 |2000-01-12 |2000-01-12 |2000-01-11] <String>
[1234       | 1234      | 1234      | 1235      | 1235      | 1234     ] <String>
[4          | 10        | 16        | 24        | 30        | 20       ] <Integer>
[7          | 13        | 19        | 27        | 34        | 25       ] <Integer>
[9          | 15        | 21        | 29        | 35        | 40       ] <Integer>

Using Java, I want to sort them by the values of the first list in descending order . If the values in the first list are equals, then sort the two equal values by the corresponding values in the second list in natural order . The strings in the second list can be sorted in natural order by calling Collection.sort(second_list).

(Example: because the elements at index 4 and 5 are equals, I have to sort them by the elements at index 4 and 5 in the second list in natural order: 123.12 = 123.12 but "2000-01-12" > "2000-01-11", so the order of the last two indexes will be 5, 4)

The sorted lists should look like these:

     0            3           5          4            1         2 

[12345.12   |1234.0     |123.12     |123.12     |123.0      |12.12     ] <Double>
[2000-01-11 |2000-01-12 |2000-01-11 |2000-01-12 |2000-01-11 |2000-01-11] <String>
[1234       | 1235      | 1234      | 1235      | 1234      | 1234     ] <String>
[4          | 24        | 20        | 30        | 10        | 16       ] <Integer>
[7          | 27        | 25        | 34        | 13        | 19       ] <Integer>
[9          | 29        | 40        | 35        | 15        | 21       ] <Integer>

I have tried to build a ArrayList of strings where each element in list contain elements from one column as we can see above (ex: the column as index 0). After each element in the column above I concatenate the string with a comma "," so that I can split the string after sorting (ex: "12345.12,2000-01-11,...,9". Becouse the sort didn't work as I expected, I have abandoned this plan.

I need a kind of a table that allows duplicate values in rows.

Maybe if the first List will be a Map where indexes are keys and values are the elements in the ArrayLists above I can do this:

• I sort the values of Map<Integer, Double> by values. Indexes - are keys, elements in first list presented - are values. So I obtain the order of indexes: 0 3 5 4 1 2
• I sort other ArrayLists by this custom order, but what I do If the values in the Map<Integer, Double> are duplicates? How do I sort them by a natural order of elements in the second List?

... I need a structure that sorts fast the Lists mentioned.

Answer 1

Create an item object with your values names:

public class Item {

    private Double value1;

    private String value2;

    private String value3;

    private Integer value4;

    private Integer value5;

    private Integer value6;

    public Double getValue1() {
        return value1;
    }

    public void setValue1(Double value1) {
        this.value1 = value1;
    }

    public String getValue2() {
        return value2;
    }

    public void setValue2(String value2) {
        this.value2 = value2;
    }

    public String getValue3() {
        return value3;
    }

    public void setValue3(String value3) {
        this.value3 = value3;
    }

    public Integer getValue4() {
        return value4;
    }

    public void setValue4(Integer value4) {
        this.value4 = value4;
    }

    public Integer getValue5() {
        return value5;
    }

    public void setValue5(Integer value5) {
        this.value5 = value5;
    }

    public Integer getValue6() {
        return value6;
    }

    public void setValue6(Integer value6) {
        this.value6 = value6;
    }        

}

And in other class use this:

public class Test {

    ArrayList<Item> items;

    public Test(){
        items = new ArrayList<>();
        this.dataList();
    }

    public void dataList(){
        Item item = new Item();
        item.setValue1(12345.12);
        item.setValue2("2000-01-11");
        // add all your values
        items.add(item);              
        // do the same for all your objects

        //Sort your list with a custom Comparator
        Collections.sort(items, new Comparator<Item>() {
            @Override
            public int compare(Item item1, Item item2) {
                return item1.getValue1().compareTo(item2.getValue1());
            }
        });        
     }
}

Answer 2

This is a sketchy implementation of a sort that uses values from several independent Comparable lists of equal length to create an order where the Lists represent the sort keys.

public static void sort( List<List<? extends Comparable>> lol ){
    List<Integer> index = new ArrayList<>();
    for( int i = 0; i < lol.get(0).size(); ++i ){
        index.add( i );
    }
    Collections.sort( index, new CompInd( lol, index) );
    for( int i: index ){
        for( int j = 0; j < lol.size(); ++j ){
            System.out.print( " " + lol.get(j).get(i) );
        }
        System.out.println();
    }
}

Class CompInd implements the Comparator for indices of the n Lists.

class CompInd implements Comparator<Integer> {
    private List<List<? extends Comparable>> comp;
    private List<Integer> index;
    public CompInd( List<List<? extends Comparable>> comp, List<Integer> index ){
        this.comp = comp;
        this.index = index;
    }

    public int compare(Integer ind1, Integer ind2){
        for( int i = 0; i < comp.size(); ++i ){
            int res = 
                comp.get(i).get(ind1).compareTo( comp.get(i).get(ind2) );
            if( res != 0 ) return res;
        }
        return 0;
    }
}

The main method creates three Lists (from your data) and calls the sort.

public static void main( String[] args ){
    List<Double> dl1 = new ArrayList<>();
    for( double d: new double[]{12345.12, 123.0, 12.12, 1234.0, 123.12, 123.12} ){
        dl1.add( d );
    }
    List<String> sl1 = new ArrayList<>();
    for( String s: new String[]{"2000-01-11","2000-01-11","2000-01-11","2000-01-12","2000-01-12","2000-01-11"} ){
        sl1.add( s );
    }
    List<String> sl2 = new ArrayList<>();
    for( String s: new String[]{"1234","1234","1234","1235","1235","1234"} ){
        sl2.add( s );
    }

    List<List<? extends Comparable>> lol = new ArrayList<>();
    lol.add( dl1 );
    lol.add( sl1 );
    lol.add( sl2 );
    sort( lol );
    }
}

This works for any number of parallel Lists, provided they are all Lists of objects implementing Comparable, of course.