C Library Functions  - sort_heap (3)

NAME
sort_heap(3f) - [M_sort:sort:heapsort] indexed sort of an array (LICENSE:PD)

CONTENTS

Synopsis
Description
Options
Returns
Example

SYNOPSIS
subroutine sort_heap(dat,indx) 

      TYPE,intent(in) :: dat
      integer,intent(out) :: indx(size(dat))

DESCRIPTION
An indexed sort of an array. The data is not moved. An integer array is generated instead with values that are indices to the sorted order of the data. This requires a second array the size of the input array, which for large arrays could require a significant amount of memory. One major advantage of this method is that any element of a user-defined type that is a scalar intrinsic can be used to provide the sort data and subsequently the indices can be used to access the entire user-defined type in sorted order. This makes this seemingly simple sort procedure usuable with the vast majority of user-defined types.

OPTIONS
DAT an array of type REAL, INTEGER, or CHARACTER(KIND=kind(’A’) to be sorted

RETURNS
INDX an INTEGER array of default kind that contains the sorted indices.

EXAMPLE
Sample usage: 

   program demo_sort_heap
   use M_sort, only : sort_heap
   implicit none
   integer,parameter            :: isz=10000
   real                         :: rr(isz)
   integer                      :: ii(isz)
   character(len=63)            :: cc(isz)
   integer                      :: indx(isz)
   integer                      :: i
   write(*,*)’initializing array with ’,isz,’ random numbers’
   CALL RANDOM_NUMBER(RR)
   rr=rr*450000.0
   ii=rr
   do i=1,size(cc)
      cc(i)=random_string(&
      & ’abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 ’, &
      & len(cc))
   enddo


   write(*,*)’checking if real values are sorted(3f)’
   call sort_heap(rr,indx)
   ! use the index array to actually move the input array into a sorted order
   rr=rr(indx)
   do i=1,isz-1
      if(rr(i).gt.rr(i+1))then
         write(*,*)’Error in sorting reals small to large ’,i,rr(i),rr(i+1)
      endif
   enddo
   write(*,*)’test of real sort_heap(3f) complete’


   write(*,*)’checking if integer values are sorted(3f)’
   call sort_heap(ii,indx)
   ! use the index array to actually move the input array into a sorted order
   ii=ii(indx)
   do i=1,isz-1
      if(ii(i).gt.ii(i+1))then
         write(*,*)’Error sorting integers small to large ’,i,ii(i),ii(i+1)
      endif
   enddo
   write(*,*)’test of integer sort_heap(3f) complete’


   write(*,*)’checking if character values are sorted(3f)’
   call sort_heap(cc,indx)
   ! use the index array to actually move the input array into a sorted order
   cc=cc(indx)
   do i=1,isz-1
      if(cc(i).gt.cc(i+1))then
         write(*,*)’Error sorting characters small to large ’,i,cc(i),cc(i+1)
      endif
   enddo
   write(*,*)’test of character sort_heap(3f) complete’


   contains


   function random_string(chars,length) result(out)


   ! create random string from provided chars


   character(len=*),intent(in)     :: chars
   integer,intent(in)              :: length
   character(len=:),allocatable    :: out
      real                         :: x
      integer                      :: ilen   ! length of list of characters
      integer                      :: which
      integer                      :: i
      ilen=len(chars)
      out=’’
      if(ilen.gt.0)then
         do i=1,length
            call random_number(x)
            which=nint(real(ilen-1)*x)+1
            out=out//chars(which:which)
         enddo
      endif
   end function random_string


   end program demo_sort_heap
Results: 

    initializing array with        10000  random numbers
    checking if real values are sorted(3f)
    test of real sort_heap(3f) complete
    checking if integer values are sorted(3f)
    test of integer sort_heap(3f) complete
    checking if character values are sorted(3f)
    test of character sort_heap(3f) complete

Nemo Release 3.1 sort_heap (3) July 22, 2023
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