[R] Please help translate this program in C++ to R

[Eric Berger]

It is fairly easy to incorporate C++ code into R programs using the
Rcpp package.
Definitely worth the effort to learn how to do this.

On Sun, Dec 15, 2019 at 5:48 AM Boris Steipe <boris.steipe using utoronto.ca> wrote:
>
> See this thread why that's a bad idea ...
>  https://stackoverflow.com/questions/26080716/merge-sort-in-r
>
> ... and use the code given there, or give us some context why a literal translation would be important to you.
>
> Cheers,
> Boris
>
>
>
>
> > On 2019-12-15, at 05:37, Александр Дубровский <dubrovvsskkyy using gmail.com> wrote:
> >
> > /* Iterative C program for merge sort */
> > #include<stdlib.h>
> > #include<stdio.h>
> >
> > /* Function to merge the two haves arr[l..m] and arr[m+1..r] of array arr[]
> > */
> > void merge(int arr[], int l, int m, int r);
> >
> > // Utility function to find minimum of two integers
> > int min(int x, int y) { return (x<y)? x :y; }
> >
> >
> > /* Iterative mergesort function to sort arr[0...n-1] */
> > void mergeSort(int arr[], int n)
> > {
> >   int curr_size;  // For current size of subarrays to be merged
> >                   // curr_size varies from 1 to n/2
> >   int left_start; // For picking starting index of left subarray
> >                   // to be merged
> >
> >   // Merge subarrays in bottom up manner.  First merge subarrays of
> >   // size 1 to create sorted subarrays of size 2, then merge subarrays
> >   // of size 2 to create sorted subarrays of size 4, and so on.
> >   for (curr_size=1; curr_size<=n-1; curr_size = 2*curr_size)
> >   {
> >       // Pick starting point of different subarrays of current size
> >       for (left_start=0; left_start<n-1; left_start += 2*curr_size)
> >       {
> >           // Find ending point of left subarray. mid+1 is starting
> >           // point of right
> >           int mid = min(left_start + curr_size - 1, n-1);
> >
> >           int right_end = min(left_start + 2*curr_size - 1, n-1);
> >
> >           // Merge Subarrays arr[left_start...mid] &
> > arr[mid+1...right_end]
> >           merge(arr, left_start, mid, right_end);
> >       }
> >   }
> > }
> >
> > /* Function to merge the two haves arr[l..m] and arr[m+1..r] of array arr[]
> > */
> > void merge(int arr[], int l, int m, int r)
> > {
> >    int i, j, k;
> >    int n1 = m - l + 1;
> >    int n2 =  r - m;
> >
> >    /* create temp arrays */
> >    int L[n1], R[n2];
> >
> >    /* Copy data to temp arrays L[] and R[] */
> >    for (i = 0; i < n1; i++)
> >        L[i] = arr[l + i];
> >    for (j = 0; j < n2; j++)
> >        R[j] = arr[m + 1+ j];
> >
> >    /* Merge the temp arrays back into arr[l..r]*/
> >    i = 0;
> >    j = 0;
> >    k = l;
> >    while (i < n1 && j < n2)
> >    {
> >        if (L[i] <= R[j])
> >        {
> >            arr[k] = L[i];
> >            i++;
> >        }
> >        else
> >        {
> >            arr[k] = R[j];
> >            j++;
> >        }
> >        k++;
> >    }
> >
> >    /* Copy the remaining elements of L[], if there are any */
> >    while (i < n1)
> >    {
> >        arr[k] = L[i];
> >        i++;
> >        k++;
> >    }
> >
> >    /* Copy the remaining elements of R[], if there are any */
> >    while (j < n2)
> >    {
> >        arr[k] = R[j];
> >        j++;
> >        k++;
> >    }
> > }
> >
> > /* Function to print an array */
> > void printArray(int A[], int size)
> > {
> >    int i;
> >    for (i=0; i < size; i++)
> >        printf("%d ", A[i]);
> >    printf("\n");
> > }
> >
> > /* Driver program to test above functions */
> > int main()
> > {
> >    int arr[] = {12, 11, 13, 5, 6, 7};
> >    int n = sizeof(arr)/sizeof(arr[0]);
> >
> >    printf("Given array is \n");
> >    printArray(arr, n);
> >
> >    mergeSort(arr, n);
> >
> >    printf("\nSorted array is \n");
> >    printArray(arr, n);
> >    return 0;
> > }
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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 using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.