Hi: I sent this yesterday but it must be out there in hyperspace somewhere because it never appeared on the R-list. Also, I had to look quicksort up because it's been too long. Anyway, your code looks similar to the java code at
http://www.algolist.net/Algorithms/Sorting/Quicksort. and I show it below. The difference is that you are calling partition recursively while the code below calls quicksort recursively. that probably makes a difference but I didn't test it. hopefully that's the problem. good luck. # quicksort Java code #================================================================ int partition(int arr[], int left, int right) { int i = left, j = right; int tmp; int pivot = arr[(left + right) / 2]; while (i <= j) { while (arr[i] < pivot) i++; while (arr[j] > pivot) j--; if (i <= j) { tmp = arr[i]; arr[i] = arr[j]; arr[j] = tmp; i++; j--; } }; return i; } void quickSort(int arr[], int left, int right) { int index = partition(arr, left, right); if (left < index - 1) quickSort(arr, left, index - 1); if (index < right) quickSort(arr, index, right); } On Sun, Sep 4, 2011 at 7:18 AM, warc <conny-cla...@gmx.de> wrote: > the error message I get is: > > Error in while (x[j] >= pivot) { : Argument has length 0 > > so either pivot or x[j] is NULL. > and it somestimes happens the first time the program enters the recursion, > sometimes the 6. or anywhere inbetween. > > > > jholtman wrote: >> >> have you tried to debug it yourself. All you said is that 'it went >> wrong'. that is not a very clear statement of the problem. If I were to >> start looking at it, I would put some print statements in it to see what >> is happening on eachpath and with each set of data. Have you tried this? >> >> Sent from my iPad >> >> On Sep 3, 2011, at 21:51, warc <conny-cla...@gmx.de> wrote: >> >>> Hey guys, >>> I tried to program quicksort like this but somethings wrong. >>> >>> please help >>> >>> >>> >>>> partition <- function(x, links, rechts){ >>>> >>>> i <- links >>>> j <- rechts >>>> t <- 0 >>>> pivot <- sample(x[i:j],1) >>>> >>>> while(i <= j){ >>>> >>>> while(x[i] <= pivot){ >>>> i = i+1} >>>> >>>> while(x[j] >= pivot){ >>>> j = j-1} >>>> >>>> if( i <= j){ >>>> >>>> t = x[i] >>>> x[i] = x[j] >>>> x[j] = t >>>> >>>> i=i+1 >>>> j=j-1 >>>> >>>> } >>>> print(pivot) >>>> >>>> >>>> } >>>> #Rekursion >>>> >>>> if(links < j){ >>>> partition(x, links, j)} >>>> if(i < rechts){ >>>> partition(x, i, rechts)} >>>> >>>> return(x) >>>> } >>>> >>>> >>>> quicksort <- function(x){ >>>> >>>> >>>> >>>> partition(x, 1, length(x)) >>>> } >>> >>> >>> >>> thx >>> >>> -- >>> View this message in context: >>> http://r.789695.n4.nabble.com/what-is-wrong-with-my-quicksort-tp3788681p3788681.html >>> Sent from the R help mailing list archive at Nabble.com. >>> >>> ______________________________________________ >>> R-help@r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-help >>> PLEASE do read the posting guide >>> http://www.R-project.org/posting-guide.html >>> and provide commented, minimal, self-contained, reproducible code. >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > > -- > View this message in context: > http://r.789695.n4.nabble.com/what-is-wrong-with-my-quicksort-tp3788681p3789080.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
