Comments on: Quicksort in Scala

By: Chris Wong

Chris Wong — Sun, 15 Nov 2009 05:12:46 +0000

Thanks for the example. Would it look similar with a list of Comparable objects rather than a specific Int type? I posted related thoughts about conciseness here, referencing this post, along with a sample Groovy implementation:

http://chriswongdevblog.blogspot.com/2009/11/on-conciseness.html

By: Rogério Liesenfeld

Rogério Liesenfeld — Sat, 14 Nov 2009 01:48:19 +0000

The last line above got truncated; it should be:

[sort(a[n | n < pivot]), a[n | n == pivot], sort(a[n | n > pivot])];

By: Rogério Liesenfeld

Rogério Liesenfeld — Sat, 14 Nov 2009 01:44:59 +0000

This is the JavaFX Script version for a QuickSort function:
function sort(a: Integer[]): Integer[] { if (sizeof a < 2) a else { def pivot = a[sizeof a / 2]; [sort(a[n | n pivot])]; } }

By: Lars Vogel

Lars Vogel — Fri, 13 Nov 2009 21:45:32 +0000

@JohnDoe: Nice & thanks. Coding updated, I also find this representation more concise.

By: JohnDoe

JohnDoe — Fri, 13 Nov 2009 21:24:53 +0000

http://www.scala-lang.org/docu/files/api/scala/Array.html

override def ++[B >: A](that : Iterable[B]) : Array[B]

Returns an array consisting of all elements of this array followed by all elements of the argument iterable.

By: Lars Vogel

Lars Vogel — Fri, 13 Nov 2009 20:22:40 +0000

@Noct: To my knowledge Scala does not define function “+” on Array. See also http://www.scala-lang.org/docu/files/api/scala/Array$object.html

By: Noct

Noct — Fri, 13 Nov 2009 20:08:20 +0000

Comparing to groovy quicksort impl:

def quickSort(lst){
if(lst.size()
if(item < pivot){ less.add(item)}
else{greater.add(item)}
}
return quickSort(less)+[pivot]+quickSort(greater)
}

I find "return quickSort(less)+[pivot]+quickSort(greater)" more concise, but you can override the + operator in scala to append lists. Or does it behave that way by default?

By: NN

NN — Fri, 13 Nov 2009 19:46:10 +0000

Is there a benchmark comparison to a java array based quicksort available?
How are the memory requirements – is the compiler able to generate bytecode that uses int[]?
What happens with a sort(sort: Array[Number])?

By: Lars Vogel

Lars Vogel — Fri, 13 Nov 2009 16:47:34 +0000

@XXX I would agree that this saves one sign and that this is good. But other then that does this makes a difference? Anyway I adjusted the code, less is more.

By: XXX

XXX — Fri, 13 Nov 2009 16:42:52 +0000

if (array.length <2) array is slightly better