C Library Functions  - prank_unique (3)

NAME
prank_unique(3f) - [M_orderpack:RANK:PARTIAL:UNIQUE] partially ranks an array removing duplicates

CONTENTS

Synopsis
Description
Options
Examples
Author
Maintainer
License

SYNOPSIS
Subroutine Prank_Unique (INVALS, IRNGT, NORD) 

     ${TYPE} (kind=${KIND}), Intent (In) :: INVALS(:)
     Integer, Intent (Out)               :: IRNGT(:)
     Integer, Intent (InOut)             :: NORD
Where ${TYPE}(kind=${KIND}) may be
o Real(kind=real32)
o Real(kind=real64)
o Integer(kind=int16)
o Integer(kind=int32)
o Integer(kind=int64)

DESCRIPTION
Partially rank INVALS() up to order NORD at most, removing duplicate entries.

Internally, this routine uses a pivoting strategy such as the one of finding the median based on the quick-sort algorithm, but we skew the pivot choice to try to bring it to NORD as quickly as possible. It uses two temporary arrays, where it stores the indices of the values smaller than the pivot (ILOWT), and the indices of values larger than the pivot that we might still need later on (IHIGT). It iterates until it can bring the number of values in ILOWT to exactly NORD, and then uses an insertion sort to rank this set, since it is supposedly small. At all times, the NORD first values in ILOWT correspond to distinct values of the input array.

OPTIONS

INVALS array to partially sort
IRNGT indices returned that point to lowest values
NORD number of sorted values to determine before eliminating duplicates

EXAMPLES
Sample program: 

   program demo_prank_unique
   ! ranks array, removing duplicates
   use M_orderpack, only : prank_unique
   implicit none
   character(len=*),parameter :: g=’(*(g0,1x))’
   integer,allocatable :: INVALS(:)
   integer,allocatable :: irngt(:)
   integer :: nord
   !
   write(*,g)’If enough values are unique, will return NORD indices’
   INVALS=[10,5,7,1,4,5,6,8,9,10,1]
   nord=5
   call printme()
   !
   write(*,g)’If not enough values are unique, will change NORD’
   INVALS=[-1,0,-1,0,-1,0,-1]
   nord=5
   if(allocated(irngt))deallocate(irngt)
   allocate(irngt(nord))
   call printme()
   !
   contains
   subroutine printme()
      write(*,g)’ORIGINAL:’,INVALS
      write(*,g)’NUMBER OF INDICES TO SORT:’,nord
      if(allocated(irngt))deallocate(irngt)
      allocate(irngt(nord))
      call prank_unique(INVALS,irngt,nord)
      write(*,g)’NUMBER OF INDICES RETURNED:’,nord
      write(*,g)’RETURNED INDICES:’,irngt(:nord)
      write(*,g)nord,’SMALLEST UNIQUE VALUES:’,INVALS(irngt(:nord))
   end subroutine
   end program demo_prank_unique
Results: 

   If enough values are unique, will return NORD indices
   ORIGINAL: 10 5 7 1 4 5 6 8 9 10 1
   NUMBER OF INDICES TO SORT: 5
   NUMBER OF INDICES RETURNED: 5
   RETURNED INDICES: 11 5 2 7 3
   5 SMALLEST UNIQUE VALUES: 1 4 5 6 7
   If not enough values are unique, will change NORD
   ORIGINAL: -1 0 -1 0 -1 0 -1
   NUMBER OF INDICES TO SORT: 5
   NUMBER OF INDICES RETURNED: 2
   RETURNED INDICES: 1 2
   2 SMALLEST UNIQUE VALUES: -1 0

AUTHOR
Michel Olagnon - Feb. 2000

MAINTAINER
John Urban, 2022.04.16

LICENSE
CC0-1.0

Nemo Release 3.1 prank_unique (3) July 22, 2023
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