Procedure

   ordi_c ( The ordinal position of an element in a set ) 

   SpiceInt ordi_c ( SpiceInt        item,
                     SpiceCell     * set   )

Abstract

   Return the ordinal position of a given item in a set. If the
   item does not appear in the set, return -1.

Required_Reading

   SETS

Keywords

   SEARCH
   SETS

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   item       I   An item to locate within a set.
   set        I   A set to search for a given item.

   The function returns the ordinal position of item within the set.

Detailed_Input

   item        is an integer value to be located within a set.

   set         is a properly validated SPICE set that is to be
               searched for the occurrence of `item'.

               `set' must be declared as an integer SpiceCell.

               CSPICE provides the following macro, which declares and
               initializes the cell

                  SPICEINT_CELL           ( set, SETSZ );

               where SETSZ is the maximum capacity of `set'.

Detailed_Output

   The function returns the ordinal position of `item' within `set'.
   Ordinal positions range from 0 to N-1, where N is the cardinality of
   the set.

   If `item' is not an element of `set', the function returns -1.

Parameters

   None.

Exceptions

   1)  If the input set has invalid cardinality, an error is signaled
       by a routine in the call tree of this routine. ordi_c returns an
       unspecified value in this case.

   2)  If the input set has invalid size, an error is signaled by a
       routine in the call tree of this routine. ordi_c returns an
       unspecified value in this case.

   3)  If the `set' cell argument has a type other than SpiceInt, the
       error SPICE(TYPEMISMATCH) is signaled. The function returns
       the value -1.

   4)  If the `set' cell argument does not qualify as a SPICE set,
       the error SPICE(NOTASET) is signaled. SPICE sets have their
       data elements stored in increasing order and contain no
       duplicate elements. The function returns the value -1.

Files

   None.

Particulars

   A natural ordering can be imposed upon the elements of any
   SPICE set, be it integer, character or double precision. For
   character strings the ASCII collating sequence serves as the
   ordering relation, for double precision and integer variables
   the arithmetic ordering is used.

   Given any element of a set, its location within this ordered
   sequence of elements is called its ordinal position within
   the set.

   In common mathematical usage, ordinal positions of elements
   in a set of cardinality N range from 1 to N. In C programs,
   it is much more convenient to use the range 0 to N-1; this is
   the convention used in CSPICE.

   For illustrative purposes suppose that set represents the set

      { 8, 1, 2, 9, 7, 4, 10 }

   The ordinal position of:

       8 is 4
       1 is 0
       2 is 1
       9 is 5
       7 is 3
       4 is 2
      10 is 6

Examples

   The numerical results shown for this example may differ across
   platforms. The results depend on the SPICE kernels used as
   input, the compiler and supporting libraries, and the machine
   specific arithmetic implementation.

   1) Obtain the ordinal positions shown in the table of the -Particulars
      section above.


      Example code begins here.


      /.
         Program ordi_ex1
      ./
      #include <stdio.h>
      #include "SpiceUsr.h"

      int main()
      {
         /.
         Declare an integer set and populate it with the elements
         shown above.
         ./
         #define MAXSIZ         7

         SPICEINT_CELL ( set,   MAXSIZ );

         SpiceInt               inputs [MAXSIZ] =
                                {
                                   8, 1, 2, 9, 7, 4, 10
                                };

         SpiceInt               expected [MAXSIZ] =
                                {
                                   4, 0, 1, 5, 3, 2, 6
                                };

         SpiceInt               i;
         SpiceInt               iElt;


         /.
         Create the set.
         ./

         for ( i = 0;  i < MAXSIZ;  i++ )
         {
            insrti_c ( inputs[i], &set );
         }

         /.
         Examine the ordinal positions of the set's elements.
         Extract each element and verify that ordi_c gives the
         index at which the element is located.
         ./

         for ( i = 0;  i < card_c(&set);  i++ )
         {
            iElt = inputs[i];

            if (  ordi_c(iElt, &set)  !=  expected[i]  )
            {
               setmsg_c ( "Position of # was expected to be # "
                          "but was actually #."                 );
               errint_c ( "#",  iElt                            );
               errint_c ( "#",  expected[i]                     );
               errint_c ( "#",  ordi_c(iElt,&set)               );
               sigerr_c ( "INVALID LOCATION"                    );
            }
            printf( "%2d  is the ordinal position of %d\n",
                     (int)expected[i], (int)iElt                );
         }

         return ( 0 );
      }


      When this program was executed on a Mac/Intel/cc/64-bit
      platform, the output was:


       4  is the ordinal position of 8
       0  is the ordinal position of 1
       1  is the ordinal position of 2
       5  is the ordinal position of 9
       3  is the ordinal position of 7
       2  is the ordinal position of 4
       6  is the ordinal position of 10

Restrictions

   None.

Literature_References

   None.

Author_and_Institution

   N.J. Bachman        (JPL)
   C.A. Curzon         (JPL)
   J. Diaz del Rio     (ODC Space)
   H.A. Neilan         (JPL)
   W.L. Taber          (JPL)
   I.M. Underwood      (JPL)

Version

   -CSPICE Version 1.0.1, 01-NOV-2021 (JDR)

       Edited the header to comply with NAIF standard. Extended code example to
       generate outputs and provided example's solution.

       Extended description of argument "set" in -Detailed_input to include
       type and preferred declaration method.

       Added entries #1 and #2 to -Exceptions section.

   -CSPICE Version 1.0.0, 07-AUG-2002 (NJB) (CAC) (HAN) (WLT) (IMU)

Index_Entries

   the ordinal position of an element in a set

Link to routine ordi_c source file ordi_c.c