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      Read a free-format ASCII file with columns of data into IDL vectors


      Lines of data not meeting the specified format (e.g. comments) are
      ignored. By default, columns may be separated by commas or spaces.
      Use READFMT to read a fixed-format ASCII file. Use RDFLOAT for
      much faster I/O (but less flexibility). Use FORPRINT to write
      columns of data (inverse of READCOL).
      If you sure that all lines meet the specified format (excluding
      commented and SKIPed lines) then the speed for reading large files
      can be significantly improved by setting the /QUICK keyword.

Calling Sequence

      READCOL, name, v1, [ v2, v3, v4, v5, ... v50 , COMMENT=, /NAN
          COUNT =, STRINGSKIP=


      NAME - Name of ASCII data file, scalar string.

Optional Input Keywords

      FORMAT - scalar string containing a letter specifying an IDL type
              for each column of data to be read. Allowed letters are
              A - string data, B - byte, D - double precision, F- floating
              point, I - short integer, L - longword, LL - 64 bit integer,
              U - unsigned short integer, UL - unsigned long integer
              Z - longword hexadecimal, and X - skip a column.
              Columns without a specified format are assumed to be floating
              point. Examples of valid values of FMT are
      'A,B,I' ;First column to read as a character string, then
                      1 column of byte data, 1 column integer data
      'L,L,L,L' ;Four columns will be read as longword arrays.
      ' ' ;All columns are floating point
      If a FORMAT keyword string is not supplied, then all columns are
      assumed to be floating point.
      /SILENT - Normally, READCOL will display each line that it skips over.
              If SILENT is set and non-zero then these messages will be
      /DEBUG - If this keyword is non-zero, then additional information is
                printed as READCOL attempts to read and interpret the file.
      COMMENT - single character specifying comment character. Any line
                beginning with this character will be skipped. Default is
                no comment lines.
      /COMPRESS - If set, then the file is assumed to be gzip compressed.
                There is no automatic recognition of compressed files
                by extension type.
      DELIMITER - Character(s) specifying delimiter used to separate
                columns. Usually a single character but, e.g. delimiter=':,'
                specifies that either a colon or comma as a delimiter.
                Set DELIM = string(9b) to read tab separated data
                The default delimiter is either a comma or a blank.
      /NAN - if set, then an empty field will be read into a floating or
                double numeric variable as NaN; by default an empty field is
                converted to 0.0.
      /PRESERVE_NULL - If set, then spaces are considered to be valid fields,
                useful if the columns contain missing data. Note that between
                April and December 2006, /PRESERVE_NULL was the default.
      /QUICK - If set, then READCOL does not check that each individual line
                matches the supplied format. This makes READCOL less
                flexible but can provide a significant speed improvement when
                reading large files.
      SKIPLINE - Scalar specifying number of lines to skip at the top of file
              before reading. Default is to start at the first line.
      NUMLINE - Scalar specifying number of lines in the file to read.
              Default is to read the entire file
      STRINGSKIP - will skip all lines that begin with the specified string.
              (Unlike COMMENT this can be more than 1 character.) Useful to
              skip over comment lines.


      V1,V2,V3,...V50 - IDL vectors to contain columns of data.
              Up to 50 columns may be read. The type of the output vectors
              are as specified by FORMAT.

Optional Output Keywords

      COUNT - integer giving the number of valid lines actually read
      NLINES - integer giving the total number of lines in the file
                (as returned by FILE_LINES)


      Each row in a file position.dat contains a star name and 6 columns
      of data giving an RA and Dec in sexagesimal format. Read into IDL
      variables. (NOTE: The star names must not include the delimiter
      as a part of the name, no spaces or commas as default.)
      IDL> FMT = 'A,I,I,F,I,I,F'
      IDL> READCOL,'position.dat',F=FMT,name,hr,min,sec,deg,dmin,dsec
      The HR,MIN,DEG, and DMIN variables will be integer vectors.
      Alternatively, all except the first column could be specified as
      floating point.
      IDL> READCOL,'position.dat',F='A',name,hr,min,sec,deg,dmin,dsec
      To read just the variables HR,MIN,SEC
      IDL> READCOL,'position.dat',F='X,I,I,F',HR,MIN,SEC


      This procedure is designed for generality and not for speed.
      If a large ASCII file is to be read repeatedly, it may be worth
      writing a specialized reader.
      Columns to be read as strings must not contain the delimiter character
      (i.e. commas or spaces by default). Either change the default
      delimiter with the DELIMITER keyword, or use READFMT to read such files.
      Numeric values are converted to specified format. For example,
      the value 0.13 read with an 'I' format will be converted to 0.

Procedures Called

      The version of STRNUMBER() must be after August 2006.

Revision History

      Written W. Landsman November, 1988
      Modified J. Bloch June, 1991
      (Fixed problem with over allocation of logical units.)
      Added SKIPLINE and NUMLINE keywords W. Landsman March 92
      Read a maximum of 25 cols. Joan Isensee, Hughes STX Corp., 15-SEP-93.
      Call NUMLINES() function W. Landsman Feb. 1996
      Added DELIMITER keyword W. Landsman Nov. 1999
      Fix indexing typos (i for k) that mysteriously appeared W. L. Mar. 2000
      Hexadecimal support added. MRG, RITSS, 15 March 2000.
      Default is comma or space delimiters as advertised W.L. July 2001
      Faster algorithm, use STRSPLIT if V5.3 or later W.L. May 2002
      Accept null strings separated by delimiter ,e.g. ',,,'
      Use SCOPE_VARFETCH instead of EXECUTE() for >V6.1 W.L. Jun 2005
      Added compile_opt idl2 W. L. July 2005
      Added the NaN keyword W. L August 2006
      Added /PRESERVE_NULL keyword W.L. January 2007
      Assume since V5.6 (FILE_LINES available ) W.L. Nov 2007
      Added COUNT output keyword W.L. Aug 2008
      Added NLINES output keyword W.L. Nov 2008
      Added SKIPSTART keyword Stephane Beland January 2008
      Renamed SKIPSTART to STRINGSKIP to keep meaning of SKIP W.L. Feb 2008
      Assume since V6.1, SCOPE_VARFETCH available W.L. July 2009
      Read up to 40 columns W.L. Aug 2009
      Use pointers instead of SCOPE_VARFETCH. Fixes bug with
      IDL Workbench and runs 20% faster Douglas J. Marshall/W.L. Nov 2009
      Recognize LL, UL, and ULL data types, don't use 'val' output from
          STRNUMBER() W.L. Feb 2010
      Graceful return even if no valid lines are present D. Sahnow April 2010
      Ability to read tab separated data WL April 2010
      Free memory used by pointers WL July 2010
      Added /QUICK keyword WL Sep 2010
      Accept normal FORTRAN formats (e.g. F5.1) P. Noterdaeme/W.L Jan 2011
      Add COMPRESS keyword, IDL 6 notation W. Landsman/J. Bailin Feb 2011
      Allow filename to be 1 element array W.Landsman/S.Antonille Apr 2011
      Feb 2010 change caused errors when reading blanks as numbers.
                          W.L. July 2012
      Read up to 50 columns W.L. March 2013

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