每列用不止一个规则对二维数组进行排序

Question

I have a two dimensional array and I want to sort it based on n criterias on different columns. This is an example:

ID   Name   GPA   
1    John   3.4
2    John   3.7
3    Aaron  3.0

Lets say I want to sort first by name then GPA it should show:

ID   Name   GPA
3    Aaron  3.0
2    John   3.7
1    John   3.4

I have the following code so far to sort it by one rule only:

Arrays.sort(a, new Comparator<String[]>() {

            @Override
            public int compare(String[] entry1, String[] entry2) {
                String time1 = entry1[n]; \\ n is provided column number
                String time2 = entry2[n]; 
                try {
                    double d1 = Double.parseDouble(time1);
                    double d2 = Double.parseDouble(time2);
                    return (int) (d1 - d2);
                }
                catch (Exception e) {
                    return time1.compareTo(time2);
                }

            }
        });

where a is my two dimensional array.. my question is, how can I sort by more than one rule? and the number of rules isnt constant as the user would provide it.

Answer 1

how can I sort by more than one rule? and the number of rules isnt constant as the user would provide it

Provide a Comparator for each column.

Then you can use the Group Comparator to combine 2 or more Comparators into a single Comparator so you can mix and match however you desire.

Answer 2

You're on the right lines with your Comparator<String[]> .

You can compose Comparator s with .thenComparing() , so you could do:

Comparator<String[]> byName = Comparator.comparing( row -> row[1] );
Comparator<String[]> byGPA = Comparator.comparing( row -> Double.parseDouble(row[2]) );

Arrays.sort(a, byName.thenComparing(byGPA));

Actually you can do this more compactly with:

Arrays.sort(a, Comparator.comparing( row -> row[1] )
                         .thenComparing( row -> Double.parseDouble(row[2])));

Working with user input, composition like this is ideal - compose at runtime based on what the user inputs.

Answer 3

I think it would be easier for you if you consider a list of objects instead of a two dimentional array.

Then you can make your object Comparable

public class Person implements Comparable {
    private Integer id;
    private String name;
    private String gpa;
    ...

    @Override
    public int compareTo(Person p) {
        // TODO Define how to compare two person
    }
}