C Library Functions - orderloc (3)

NAME

orderloc(3f) - [M_orderpack:FRACTILE] Return INDEX of Nth ordered value of array (Quick-Sort-like)

Synopsis
Description
Options
Returns
Examples
Author
Maintainer
License

SYNOPSIS

Function OrderLoc (INVALS, NORD)
      ${TYPE} (kind=${KIND}), Intent (In) :: INVALS(:)
      Integer                             :: orderloc
      Integer, Intent (In)                :: NORD
Where ${TYPE}(kind=${KIND}) may be

o Real(kind=real32)

o Real(kind=real64)

o Integer(kind=int32)

DESCRIPTION

orderloc(3f) returns the index of NORDth value of INVALS, i.e. the fractile of order NORD/SIZE(INVALS).
That is, the result is the same as sorting the array first and then returning the value INVALS(NORD).
Internally orderloc(3f) 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 fast 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 finds the maximum of this set.

OPTIONS

INVALS array to search

NORD indicates the Nth ordered value to search for

RETURNS

orderloc
the index of INVALS() that contains the requested value

EXAMPLES

Sample program:

   program demo_orderloc
   ! find Nth lowest ordered value in an array without sorting entire array
   use M_orderpack, only : orderloc
   use M_orderpack, only : medianloc
   implicit none
   integer,allocatable :: iarr(:)
   character(len=*),parameter :: list= ’(*(g0:,", "))’,sp=’(*(g0,1x))’
   integer :: i
   integer :: indx
      iarr=[80,70,30,40,50,60,20,10,0,-100]
      print list, ’ORIGINAL:’,iarr
      ! like minloc(3f) and maxloc(3f)
      print sp,’minloc’,orderloc(iarr,1),                minloc(iarr)
      print sp,’maxloc’,orderloc(iarr,size(iarr)),       maxloc(iarr)
      ! can find median
      call medianloc(iarr,indx)
      print sp,’median’,orderloc(iarr,(size(iarr)+1)/2), indx
      ! but more general so can find location of the Nth lowest value ...
      !
      ! sort the hard way, finding location of Nth value one at a time
      do i=1,size(iarr)
         write(*,sp,advance=’no’) iarr(orderloc(iarr,i))
      enddo
      print *
   end program demo_orderloc

Results:

ORIGINAL:, 80, 70, 30, 40, 50, 60, 20, 10, 0, -100 minloc 10 10 maxloc 1 1 median 3 3 -100 0 10 20 30 40 50 60 70 80

AUTHOR

Michel Olagnon - Aug. 2000

MAINTAINER

John Urban, 2022.04.16

LICENSE

CC0-1.0

Nemo Release 3.1

orderloc (3)

July 22, 2023

Generated by manServer 1.08 from 0e3e01e7-dddd-4f41-87e9-4debf871f0f2 using man macros.

INVALS	array to search
NORD	indicates the Nth ordered value to search for

orderloc
	the index of INVALS() that contains the requested value