3.3 ASCII Tables

  The most general format may be simply an ASCII text file with data stored as columns of numbers. These ASCII table files can be used to store (for example) vectors of wavelengths, fluxes, and data quality flags. One nice thing about ASCII files is that you can e-mail them anywhere. They do not need to be FTPed in binary format or converted when copied to other operating systems. Note, however, that they can get large!

You may write your vectors out as an ASCII table, with the data arranged in columns using ASC_WRITE:

ASC_WRITE,'FILENAME',P1,p2,p3,p4,...,p15 

FILENAME	The full file name of the output file to be created. If no extension is specified, .TXT is assumed.
P1	Vector to write in column 1.
p2...p15	Vector(s) to write in columns 2 through 15 (optional; include as many as many as you wish). They must have at least as many elements as P1 (all columns will be the same length as P1 which means that longer vectors will be truncated).

To read an ASCII table (not necessarily written by ASC_WRITE):

ASC_READ,'FILENAME',P1,p2,...,p15,sl=sl,ll=ll,nel=nel, $
/silent,/dbl 

FILENAME	Name of ASCII table file to read. If no extension is included, .TXT is assumed.
P1	First column of table.
p2...p15	Second through fifteenth columns, as needed.
sl	(SL) Starting line to read. This allows you to skip column headings.
ll	(LL) Last line to read. Default is to read the entire file.
nel	(NEL) Number of lines to read. Default is to read the entire file, up to 2500 lines.
silent	suppresses standard print statements.
dbl	keyword to interpret numbers as double precision rather than single precision floating point numbers.

Both ASC_READ and ASC_WRITE assume the input parameters are all vectors of similar length and contain only numbers (i.e., string arrays are not allowed.) All values read by ASC_READ are returned as floating point vectors unless the "/DBL" keyword is used to read numbers using double precision. Table 3.2 contains examples of both ASC_READ and ASC_WRITE.

   

Table 3.2: I/O Routines for Ascii Files

Expression	Definition
ASC_WRITE,'data.lis',a,b,c,d,e	Writes five vectors (a, b, c, d, and e) to DATA.LIS in columnar format.
ASC_READ,'data.lis',a,b,c,/dbl	Read first 3 columns of numbers in DATA.LIS into double precision vectors called a, b, and c.
ASC_READ,'lc.lis',day,mag,sl=3	Reads two columns of numbers in LC.LIS into IDL vectors called day and mag, starting at line three of LC.LIS and stopping at the end of the file.
ASC_READ,'lc2.lis',d2,m2,sl=3,ll=700	Reads two columns of numbers in LC2.LIS into IDL vectors called d2 and m2, starting at line three and ending with line 700.
ASC_READ,'lc3.lis',d3,m3,nel=3000	Reads two columns of numbers in LC3.LIS into IDL vectors called d3 and m3. Up to 3000 numbers per vector will be read.