uniinv Interface

Rank_Decreasing(3f) - [M_orderpack:RANK:UNIQUE] ranks an array
in decreasing order, with duplicate entries assigned the same
rank(Merge-Sort)

 Subroutine Rank_Decreasing (INVALS, IGOEST)

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

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)
   o Character(kind=selected_char_kind("DEFAULT"),len=*)

RANK_DECREASING(3f) generates an inverse ranking of an array, but
with duplicate entries assigned the same rank.

Internally, the routine is similar to pure merge-sort ranking, but on
the last pass, it sets indices in IGOEST to the rank of the original
value in an ordered set with duplicates removed. For performance
reasons, the first two passes are taken out of the standard loop,
and use dedicated coding.

 INVALS     array to rank
 IGOEST     returned rank array

program demo_rank_decreasing
! rank input array ranking duplicates the same
use M_orderpack, only : rank_decreasing
implicit none
character(len=*),parameter :: fmt='(a,*(g3.3,1x))'
integer,allocatable,dimension(:) :: INVALS, igoest, distinct, count
integer :: imx, i
   ! create an input array
   INVALS=[11, 11, 22, 11, 33, 33, 22, 33, 33]
   ! make an index array of the same size
   if(allocated(igoest))deallocate(igoest)
   allocate(igoest(size(INVALS)))
   print fmt, 'Original:                 ',INVALS
   print fmt, 'Number of indices to sort:',size(INVALS)
   ! rank input array ranking duplicates the same
   call rank_decreasing(INVALS,igoest)
   print fmt, 'Returned Indices:         ',igoest(:)
   !
   ! interrogate the results
   !
   imx=maxval(igoest)
   print fmt, 'Number of unique indices :',imx
   ! squeeze it down to just IMX unique values
   count=[(0,i=1,imx)] ! count how many times a value occurs
   distinct=count      ! array to set of unique values
   do i=1,size(INVALS)
      distinct(igoest(i))=INVALS(i)
      count(igoest(i))= count(igoest(i))+1
   enddo
   print fmt, 'Sorted unique values:     ',distinct
   print fmt, 'count of occurrences:     ',count
end program demo_rank_decreasing

Original:                  11  11  22  11  33  33  22  33  33
Number of indices to sort:  9
Returned Indices:           1   1   2   1   3   3   2   3   3
Number of unique indices :  3
Sorted unique values:      11  22  33
count of occurrences:       3   2   4

Michel Olagnon, 2000-2012

John Urban, 2022.04.16

CC0-1.0