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C Library Functions  - rank (3)

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NAME

rank(3f) - [M_orderpack:RANK] produces an INDEX that sorts an input array (optimized merge-sort)

CONTENTS

Synopsis
Description
Options
Examples
Author
Maintainer
License

SYNOPSIS

Subroutine Rank (INVALS, IRNGT)

      ${TYPE} (kind=${KIND}), Intent (In) :: INVALS(:)
      Integer, Intent (Out)               :: IRNGT(:)

Where ${TYPE}(kind=${KIND}) may be

o	Real(kind=real32)
o	Real(kind=real64)
o	Integer(kind=int32)
o	Character(kind=selected_char_kind("DEFAULT"),len=*)

DESCRIPTION

RANK(3f) ranks an input array; i.e. it produces an index of the input array elements that can order the input array in ascending order.

The ranks can be used to sort the input array, or other associated arrays or components of user types.

Internally, it uses an optimized and modified version of merge-sort. For performance reasons, the first two passes are taken out of the standard loop, and use dedicated coding.

OPTIONS

INVALS	The array to sort
IRNGT	The rank index returned

EXAMPLES

Sample program:

   program demo_rank
   ! create an index that can order an array in ascending order
   use M_orderpack, only : rank
   implicit none
   character(len=*),parameter :: g=’(*(g0,1x))’
   integer,parameter             :: dp=kind(0.0d0)
   integer,parameter             :: isz=10000
   real(kind=dp)                 :: dd(isz)
   real(kind=dp)                 :: pp
   integer                       :: indx(isz)
   integer                       :: i,j,k
   character(len=:),allocatable  :: strings(:)
   integer,allocatable           :: cindx(:)
      ! make some random numbers
      call random_seed()
      call random_number(dd)
      dd=dd-0.50_dp
      k=int(log(huge(0.0_dp))/log(2.0_dp))-1
      do i=1,isz
         call random_number(pp)
         j=floor((k+1)*pp)
         dd(i)=dd(i)*(2.0_dp**j)
      enddo
      ! rank the numeric data
      call rank(dd,indx)
      ! check order
      do i=1,isz-1
         if(dd(indx(i)).gt.dd(indx(i+1)))then
            write(*,g)’ERROR: data not sorted i=’,i,’index=’,indx(i), &
            & ’values ’,dd(indx(i)),dd(indx(i+1))
            stop 1
         endif
      enddo
      ! sort data using rank values
      dd=dd(indx)
      write(*,g)’sorted ’,isz,’values’
      write(*,g)’from’,dd(1),’to’,dd(isz)
      write(*,*)minval(dd).eq.dd(1)
      write(*,*)maxval(dd).eq.dd(isz)
      write(*,*)minloc(dd).eq.1
      write(*,*)maxloc(dd).eq.isz
      ! do a character sort
      strings= [ character(len=20) ::                               &
      & ’red’,    ’green’, ’blue’, ’yellow’, ’orange’,   ’black’, &
      & ’white’,  ’brown’, ’gray’, ’cyan’,   ’magenta’,           &
      & ’purple’]
      if(allocated(cindx))deallocate(cindx);allocate(cindx(size(strings)))

      write(*,’(a,8(a:,","))’)’BEFORE ’,&
              & (trim(strings(i)),i=1,size(strings))

      call rank(strings,cindx)

      write(*,’(a,8(a:,","))’)’SORTED ’,&
              & (trim(strings(cindx(i))),i=1,size(strings))

      strings=strings(cindx) ! sort the array using the rank index

      do i=1,size(strings)-1
         if(strings(i).gt.strings(i+1))then
            write(*,*)’Error in sorting strings a-z’
         endif
      enddo
   end program demo_rank

Results:

   sorted  10000 values
   from -.4206770472235745E+308 to .3500810518521505E+308

    T

    T

    T

    T

BEFORE red,green,blue,yellow,orange,black,white,brown, gray,cyan,magenta,purple SORTED black,blue,brown,cyan,gray,green,magenta,orange, purple,red,white,yellow

AUTHOR

Michel Olagnon, 2000-2012

MAINTAINER

John Urban, 2022.04.16

LICENSE

CC0-1.0

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Nemo Release 3.1

rank (3)

February 23, 2025

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