Sort a two dimensional String array with Arrays.sort based on a chosen column

Question

I have a two dimensional array filled with strings in Java. I want to be able to sort the entire array relative to the column I have chosen to sort by.

For Example:

Say I have an Array of data that looks like this.

|John  | C | Doe    |

|Sally | A | Miller |

|Chris | B | Sanders|

I specify that I want to sort in descending order based on their middle initial and am returned an array that looks like this.

|John  | C | Doe    |

|Chris | B | Sanders|

|Sally | A | Miller |

Is there a way to designate a Comparator that will do this?

Andy Turner · Accepted Answer · 2015-11-25 14:07:29Z

1

Sure, just pass the column index in as a parameter of the comparator.

class ColumnComparator<T extends Comparable<T>> implements Comparator<T[]> {
  private final int column;

  ColumnComparator(int column) { this.column = column; }

  @Override public int compare(T[] a, T[] b) {
    return a[column].compareTo(b[column]);
  }
}

or, more simply, if it is always column 1 and string arrays:

class ColumnComparator implements Comparator<String[]> {
  @Override public int compare(T[] a, T[] b) {
    return a[1].compareTo(b[1]);
  }
}

answered Nov 25, 2015 at 14:07

Andy Turner

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3 Comments

Crinkley Crewms Over a year ago

Another quick question. Would this still work in a Java 6 implementation?

Andy Turner Over a year ago

I don't see why it wouldn't. Generics came in Java 5; Comparator and Comparable were both in Java 1.2.

Crinkley Crewms Over a year ago

Thank you for the quick and informative response :)

AbhinavRanjan · Accepted Answer · 2015-11-25 14:19:18Z

0


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

public class Main {
    public static void main(String[] args) {
        String[][] array = {{"John", "C", "Doe"}, {"Sally", "A", "Miller"}, {"Chris", "B", "Sanders"}};
        Arrays.sort(array, new IndexComparator(0));
        for(int i = 0; i < array.length; i++) {
            System.out.println(array[i][0]);
        }
    }
}


class IndexComparator implements Comparator {
    private int index = 0;

    public IndexComparator(int index) {
        this.index = index;
    }


    @Override
    public int compare(String[] o1, String[] o2) {
        return o1[index].compareTo(o2[index]);
    }
}

answered Nov 25, 2015 at 14:19

AbhinavRanjan

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