Manual Reference Pages - sort_shell (3)

NAME

sort_shell(3f) - [M_sort] Generic subroutine sorts the array X using Shell’s method

Synopsis
Description
Options
Example
Reference
Author

SYNOPSIS

subroutine sort_shell(lines,order[,startcol,endcol])

    character(len=*),intent(inout) :: lines(:)
    character(len=*),intent(in)    :: order
    integer,optional,intent(in)    :: startcol, endcol

subroutine sort_shell(ints,order)

    integer,intent(inout)          :: ints(:)
    character(len=*),intent(in)    :: order

subroutine sort_shell(reals,order)

    real,intent(inout)             :: reals(:)
    character(len=*),intent(in)    :: order

subroutine sort_shell(complexs,order,type)

    character(len=*),intent(inout) :: lines(:)
    character(len=*),intent(in)    :: order
    character(len=*),intent(in)    :: type

DESCRIPTION

subroutine sort_shell(3f) sorts an array over a specified field in numeric or alphanumeric order.
From Wikipedia, the free encyclopedia:
The step-by-step process of replacing pairs of items during the shell sorting algorithm. Shellsort, also known as Shell sort or Shell’s method, is an in-place comparison sort. It can be seen as either a generalization of sorting by exchange (bubble sort) or sorting by insertion (insertion sort).[3] The method starts by sorting pairs of elements far apart from each other, then progressively reducing the gap between elements to be compared. Starting with far apart elements, it can move some out-of-place elements into position faster than a simple nearest neighbor exchange. Donald Shell published the first version of this sort in 1959.[4][5] The running time of Shellsort is heavily dependent on the gap sequence it uses. For many practical variants, determining their time complexity remains an open problem.
Shellsort is a generalization of insertion sort that allows the exchange of items that are far apart. The idea is to arrange the list of elements so that, starting anywhere, considering every hth element gives a sorted list. Such a list is said to be h-sorted. Equivalently, it can be thought of as h interleaved lists, each individually sorted.[6] Beginning with large values of h, this rearrangement allows elements to move long distances in the original list, reducing large amounts of disorder quickly, and leaving less work for smaller h-sort steps to do. If the file is then k-sorted for some smaller integer k, then the file remains h-sorted. Following this idea for a decreasing sequence of h values ending in 1 is guaranteed to leave a sorted list in the end.

F90 NOTES:

o procedure names are declared private in this module so they are not accessible except by their generic name

o procedures must include a "use M_sort" to access the generic name SORT_SHELL

o if these routines are recompiled, routines with the use statement should then be recompiled and reloaded.

OPTIONS

Usage:

X input/output array to sort of type CHARACTER, INTEGER, REAL, DOUBLEPRECISION, COMPLEX, or DOUBLEPRECISION COMPLEX. order sort order o A for Ascending (a-z for strings, small to large for values) o D for Descending (z-a for strings, large to small for values, default)

FOR CHARACTER DATA:

startcol character position in strings which starts sort field. Only applies to character values. Defaults to 1. Optional. endcol character position in strings which ends sort field Only applies to character values. Defaults to end of string. Optional.

FOR COMPLEX AND COMPLEX(KIND=KIND(0.0D0)) DATA:

type Sort by

R for Real component, I for Imaginary component, S Sqrt(R**2+I**2)

EXAMPLE

Sample program

      program demo_sort_shell
      use M_sort, only : sort_shell
      character(len=:),allocatable :: array(:)

      array= [ character(len=20) ::                               &
      & ’red’,    ’green’, ’blue’, ’yellow’, ’orange’,   ’black’, &
      & ’white’,  ’brown’, ’gray’, ’cyan’,   ’magenta’,           &
      & ’purple’]

      write(*,’(a,*(a:,","))’)’BEFORE ’,(trim(array(i)),i=1,size(array))
      call sort_shell(array,order=’a’)
      write(*,’(a,*(a:,","))’)’A-Z    ’,(trim(array(i)),i=1,size(array))
      do i=1,size(array)-1
         if(array(i).gt.array(i+1))then
            write(*,*)’Error in sorting strings a-z’
         endif
      enddo

      array= [ character(len=20) ::                               &
      & ’RED’,    ’GREEN’, ’BLUE’, ’YELLOW’, ’ORANGE’,   ’BLACK’, &
      & ’WHITE’,  ’BROWN’, ’GRAY’, ’CYAN’,   ’MAGENTA’,           &
      & ’PURPLE’]

      write(*,’(a,*(a:,","))’)’BEFORE ’,(trim(array(i)),i=1,size(array))
      call sort_shell(array,order=’d’)
      write(*,’(a,*(a:,","))’)’Z-A    ’,(trim(array(i)),i=1,size(array))
      do i=1,size(array)-1
         if(array(i).lt.array(i+1))then
            write(*,*)’Error in sorting strings z-a’
         endif
      enddo

      end program demo_sort_shell

Expected output

BEFORE red,green,blue,yellow,orange,black,white,brown,gray,cyan,magenta,purple A-Z black,blue,brown,cyan,gray,green,magenta,orange,purple,red,white,yellow BEFORE RED,GREEN,BLUE,YELLOW,ORANGE,BLACK,WHITE,BROWN,GRAY,CYAN,MAGENTA,PURPLE Z-A YELLOW,WHITE,RED,PURPLE,ORANGE,MAGENTA,GREEN,GRAY,CYAN,BROWN,BLUE,BLACK

REFERENCE

1. ALGORITHM 201, SHELLSORT, J. BOOTHROYD, CACM VOL. 6, NO. 8, P 445, (1963)

2. D. L. SHELL, CACM, VOL. 2, P. 30, (1959)

AUTHOR

John S. Urban, 19970201

sort_shell (3)

October 17, 2020

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