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Sorting an array of doubles

Posted on 1998-09-03
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Last Modified: 2011-04-14
I'm confronting the problem to sort an array that contains atomic doubles not the objects Double. My question now is whether it is possible to do that in Java using the quicksort algorithm. My trials failed. Probably, since it is not possible to pass an array like a pointer like one can do in C/C++. I don't like to wrap all doubles into Double object because of perfomance lack. The I had to wrap all doubles into Doubles and after the sorting I had to unwrap the sorted Objects into the old array. Another possibility was to use a native call but I think this would be too clumsy. Any help will be appreciated.
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Question by:trouvain
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diakov earned 200 total points
ID: 1223430
I think that the internal types in Java are internal mainly because of performance considerations. So why not swap double values? I believe you can make a benchmark and see whether it is relevant. (I mean wrapping and unwrapping versus double values).
If you're so relluctant to swap dowbles, you can also use an array of int indices pointing in the array of doubles. This way you swap int's which is the same as swaping pointers in C. At the end you need only one pass with O(N) to get them ordered from the array.

Cheers.
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by:fontaine
ID: 1223431
You should have a look at the Java Generic collection Library (JGL) http://www.objectspace.com/jgl/. It contains all kind of ready to use algorithms, carefully
designed to be efficient.
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by:trouvain
ID: 1223432
I'm not reluctant to swap doubles how else should I sort an array? I overworked the quicksort algorithm and found the mistake. I only was mischieved by the idea that swapping values in an array doesn't work in Java because of the referencing approach.

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by:trouvain
ID: 1223433
Dear fontaine,

thank you for giving the link to objectspace, it was much more helpful than the given answer!
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by:diakov
ID: 1223434
Tell me how to return the points, please.
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