FTSORT

      Sort a FITS ASCII table according to a specified field

      FTSORT,h,tab,[field, REVERSE = ]               ;Sort original table header and array
               or
      FTSORT,h,tab,hnew,tabnew,[field, REVERSE =]   ;Create new sorted header

      H - FITS header (string array)
      TAB - FITS table (byte array) associated with H.  If less than 4
               parameters are supplied, then H and TAB will be updated to
               contain the sorted table

      FIELD - Field name(s) or number(s) used to sort the entire table.
              If FIELD is a vector then the first element is used for the
              primary sort, the second element is used for the secondary
              sort, and so forth.   (A secondary sort only takes effect when
              values in the primary sort  field are equal.)  Character fields
              are sorted using the ASCII collating sequence.  If omitted,
              the user will be prompted for the field name.

      HNEW,TABNEW - Header and table containing the sorted tables

      Sort a FITS ASCII table by the 'DECLINATION' field in descending order
      Assume that the table header htab, and array, tab, have already been
      read (e.g. with READFITS or FITS_READ):
      IDL> FTSORT, htab, tab,'DECLINATION',/REVERSE

       REVERSE - If set then the table is sorted in reverse order (maximum
              to minimum.    If FIELD is a vector, then REVERSE can also be
              a vector.   For example, REVERSE = [1,0] indicates that the
              primary sort should be in descending order, and the secondary
              sort should be in ascending order.

       A HISTORY record is added to the table header.

      Written W. Landsman                         June, 1988
      Converted to IDL V5.0   W. Landsman   September 1997
      New FTINFO calling sequence, added REVERSE keyword, allow secondary sorts
                  W. Landsman   May 2000

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