Comments on: Sorting a 2-Dimensional Array in Java

By: Kole Black

Kole Black — Wed, 25 Jan 2012 05:36:50 +0000

Great article post.Much thanks again. Really Cool.

By: Nitin

Nitin — Wed, 25 May 2011 11:57:27 +0000

I don't think so, it seems to be inspired from the original comment from Lars. Mark, or in fact Lars, will be able to throw some more light.

By: Thomas

Thomas — Tue, 24 May 2011 01:17:55 +0000

So why is it that

Collections.sort(Arrays.asList(data))

is faster than

Arrays.sort(data)

Can that really be?

By: Nitin

Nitin — Thu, 12 May 2011 20:39:41 +0000

Cool, I appreciate you for sharing your work with the readers here. . Added a link to it in the post for easy access.

By: Mark

Mark — Thu, 12 May 2011 20:06:55 +0000

Quite often in multidimensional arrays, you may want to do a secondary sort on another column. For example, sort first on last name, then on first name if the last names are the same.

Here are a couple extensions to Lars Feb 23, 2010 posting. I apologize in advance that some of the html might get eaten by the browser.

The following code first is a copy of Lars’ posting, followed by code for sorting on two columns, then a third example on sorting by an arbitrary number of columns, using an array of column numbers as the input.

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class TwoDcolumnComparator {
public static < T extends Comparable> void sort(final T [][] toSort,final int onColumn) {
List list = Arrays.asList(toSort);
Collections.sort(
list, new Comparator(){
public int compare(T[] a, T[] b) {
return a[onColumn].compareTo(b[onColumn]);
}
}
);
}
public static < T extends Comparable> void sort(final T [][] toSort,final int onColumn1, final int onColumn2) {
List list = Arrays.asList(toSort);
Collections.sort(
list, new Comparator(){
public int compare(T[] a, T[] b) {
if (a[onColumn1].compareTo(b[onColumn1]) == 0) {
return a[onColumn2].compareTo(b[onColumn2]);
} else {
return a[onColumn1].compareTo(b[onColumn1]);
}
}
}
);
}
public static < T extends Comparable> void sort(final T [][] toSort,final int []onColumn) {
List list = Arrays.asList(toSort);
Collections.sort(
list, new Comparator(){
public int compare(T[] a, T[] b) {
for (int i = 0;i < onColumn.length-1;i++){
if (a[onColumn[i]].compareTo(b[onColumn[i]]) != 0) {
return a[onColumn[i]].compareTo(b[onColumn[i]]);
}
}
return a[onColumn.length].compareTo(b[onColumn.length]);
}
}
);
}
}

By: amit

amit — Wed, 08 Dec 2010 08:29:16 +0000

Really helpful article

By: Line

Line — Sun, 22 Aug 2010 05:19:18 +0000

The solution is really helpful and I cannot imagine that I can make benefit of
comparator to deal with array object by itself ..

Thank you very much Nitin .

By: agil

agil — Sun, 13 Jun 2010 17:40:40 +0000

Hello Nitin,

Your solution very useful for two Dimensional array with same length.
My question is, can we sort two dimensional array based on some row and based on data length. for example we have an array {{”c”}, {”c”}, {”c”, “d”},{”c”, “a”},{”b”}}. how to get the sorted array like this {{”b”},{”c”},{”c”},{”c”,”a”},{”c”, “d”}}.

Thx a lot Nitin.

By: Bizunas

Bizunas — Sat, 29 May 2010 14:20:59 +0000

Thanks, it helped me alot. No changes needed at all

By: autofei

autofei — Fri, 28 May 2010 16:24:01 +0000

I just post a working version modified from Lars version. Hope it helpful.