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NEWBIE: How to re-sort two-dimensional int array?

Posted on 2006-07-06
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Last Modified: 2010-03-31
Dear Experts,

Another lazy question...

I have this two-dimensional int array, sorted by the first index:

int[][] myArray = new int[4][2];

With these values:

1  745
2  123
3  999
4  876

What's the easiest (laziest) way to re-sort it by the second index, so I get this:

2  123
1  745
4  876
3  999

Thanks!
BrianMc1958

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Question by:BrianMc1958
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13 Comments
 
LVL 16

Expert Comment

by:imladris
ID: 17053550
Easiest way is probably to use a variation of what you used to sort by the "first index". Since there are dozens of ways to do these kinds of things, it would probably be best if you explained and/or posted code of your existing sort.
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Author Comment

by:BrianMc1958
ID: 17053655
I'm reading data from a text file, say of customer information.  The first index in my array is simply an increment (1, 2, 3...).  The second index holds a value (say, customer age.)  I want to retain the original values in the original order, but also have a secondary, sorted array, so I can read through the result sorted by customer age.

In this case, quick-and-dirty is fine.  It's just an in-house thing, sorting just a couple dozen fields...
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Author Comment

by:BrianMc1958
ID: 17053676
So to answer your question, I'm not sorting the first time.  I'm just incrementing.  Now I have to sort.
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Accepted Solution

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Webstorm earned 250 total points
ID: 17053685
Hi BrianMc1958,

You can use :

    java.util.Arrays.sort(myArray,
         new java.util.Comparator(){
              public int compare(Object o1,Object o2)
              { return ((int[])o1)[1]-((int[])o2)[1];  }});
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Author Comment

by:BrianMc1958
ID: 17053746
To Webstorm:  I'm trying it, but getting funny results...  
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Author Comment

by:BrianMc1958
ID: 17053785
It looks (vaguely) like it's subtracting one from my first index, and not actually sorting...
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Expert Comment

by:Webstorm
ID: 17053820
it's the comparator : comparing two value o1 and o2
each are int[], comparing  o1[1] with o2[1]
Comparator.compare must return an integer value :
   <0   when first < second
   =0   when first = second    
   >0   when first > second    
-> same as first - second

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Author Comment

by:BrianMc1958
ID: 17053825
Whoops!  Sorry.  You were right.  (I had swapped my indices at one point...)

Thanks a lot!
--BrianMc1958
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LVL 35

Expert Comment

by:girionis
ID: 17053830
Try this:

int[][] myArray = {{1, 745}, {2, 123},{3, 999},{4, 876}};
        int temp = 0;
        System.out.println(myArray.length);
        for (int i=0; i<myArray.length; i++)
        {
            temp = myArray[i][1];
            if ((i+1 < myArray.length) && (myArray[i][1] > myArray[i+1][1]))
            {
                myArray[i][1] = myArray[i+1][1];
                myArray[i+1][1] = temp;
            }
           
        }

Not the best solution but it works (I hope)
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LVL 13

Expert Comment

by:Webstorm
ID: 17053837
>> I'm trying it, but getting funny results...  
what are thoses funny results ?
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LVL 13

Expert Comment

by:Webstorm
ID: 17053851
:-)
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Author Comment

by:BrianMc1958
ID: 17053858
Our messages crossed.  (Also, girionis posted in the mean time...)  

I was just mistaken.  It's working correctly now except for one row, which I'm looking into.  I'll post a follow-up if I have to.  Thanks again.  
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LVL 35

Expert Comment

by:girionis
ID: 17053889
My code will work for your array, if you run it with more values it will probably fail. Better to follow Webstorm's suggestion or try to hack my example.
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