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      Routine to extract columns from a FITS (binary or ASCII) table.

Calling Sequence

      FTAB_EXT, name_or_fcb, columns, v1, [v2,..,v50, ROWS=, EXTEN_NO= ]


      name_or_fcb - either a scalar string giving the name of a FITS file
              containing a (binary or ASCII) table, or an IDL structure
              containing as file control block (FCB) returned by FITS_OPEN
              If FTAB_EXT is to be called repeatedly on the same file, then
              it is quicker to first open the file with FITS_OPEN, and then
              pass the FCB structure to FTAB_EXT
      columns - table columns to extract. Can be either
              (1) String with names separated by commas
              (2) Scalar or vector of column numbers


      v1,...,v50 - values for the columns. Up to 50 columns can be extracted

Optional Input Keywords

      ROWS - scalar or vector giving row number(s) to extract
              Row numbers start at 0. If not supplied or set to
              -1 then values for all rows are returned. This keyword
              works for ASCII tables and binary tables where every column has
              the same number of elements, but not for variable length
              binary tables.
      EXTEN_NO - Extension number to process. If not set, then data is
              extracted from the first extension in the file (EXTEN_NO=1)


      Read wavelength and flux vectors from the first extension of a
      FITS file, 'spec.fit'. Using FTAB_HELP,'spec.fit' we find that this
      information is in columns named 'WAVELENGTH' and 'FLUX' (in columns 1
      and 2). To read the data
      IDL> ftab_ext,'spec.fit','wavelength,flux',w,f
      IDL> ftab_ext,'spec.fit',[1,2],w,f

Procedures Called



      version 1 W. Landsman August 1997
      Improve speed processing binary tables W. Landsman March 2000
      Use new FTINFO calling sequence W. Landsman May 2000
      Don't call fits_close if fcb supplied W. Landsman May 2001
      Use STRSPLIT to parse column string W. Landsman July 2002
      Cleanup pointers in TBINFO structure W. Landsman November 2003
      Avoid EXECUTE() if V6.1 or later W. Landsamn December 2006
      Assume since V6.1 W. Landsman June 2009
      Read up to 30 columns W.L. Aug 2009
      Setting ROWS = -1 should work as documented, accept up to 50
              columns W.L. Oct 2013

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