STScI Logo

ttools tables


SEE_ALSO

This package contains tasks for working with tables. Tables are files that contain data in row & column format. The supported table formats are FITS, STSDAS, and ASCII text. Different columns may have different data types, but all the values in one column have the same data type. In addition to the tabular data, a table may contain header parameters identified by keywords.

Each column has the following four items of information:
    (1) a name (case insensitive),
    (2) data type (real, double, integer, short int, boolean, or text),
    (3) a format specification for printing the contents of the column,
    (4) "units", a string (default is null).

For STSDAS tables the column names and units can be up to 20 characters in length. For FITS tables the limit is 68 characters. The default column names for ASCII tables are "c1", "c2", "c3", etc.; however, there is a "#c" syntax for giving explicit column definitions, which is described below.

Header parameters may have data types of floating point, integer, boolean, or text. Header keywords are limited to eight characters (for FITS compatibility) and are converted to upper case.

The print formats are discussed below.

Here is a list of the ttools tasks organized by function:

    create a table:
	tcreate, tedit

    display contents:
	tprint, tread, tedit, tcheck, thedit, thselect, tupar, gtedit

    modify contents:
	tedit, thedit, tupar, gtedit

    information about a table:
	tinfo, tlcol

    database-like utilities:
	tquery, tsort, tproject, tselect, tdiffer, tjoin, tmatch,
	tmerge, tproduct, texpand

    statistics, etc:
	thistogram, tlinear, trebin, tstat

    arithmetic:
	tcalc, tunits, tintegrate

    convert between table or image header parameter, cl parameter, table datum:
	keypar, keytab, parkey, partab, tabkey, tabpar, keyselect

    convert columns of arrays to other formats:
	txtable, tximage, titable, tiimage, taextract, tainsert

    change column definition or table size:
	tchcol, tchsize

    miscellaneous:
	tcopy, tdelete

ASCII text tables can be simple files (just data in row and column format), or they can have header keywords and/or explicit column definitions.

Header keywords and column definitions in text tables have the following syntax:

#k keyword = value comment
#c column_name data_type print_format units

The "#k " (or "#K ") must be the first three characters of the line, and the space following "k" is required. Header keywords can be added to any text table, and they do not have to precede the data. For a text string keyword, quotes around the value are needed if there is a comment, in order to distinguish value from comment.

The "#c " (or "#C ") must be the first three characters of the line, and the space following "c" is required. All column definitions must precede the table data. Aside from the "#c ", the syntax is the same as the output from tlcol or the tcreate.cdfile. Only the column name is required, although in most cases you will also need to give the data type (the default is d, double precision). The print format is not used for reading the text file, only for displaying it or printing it out if it was modified. The file is read in free format, with whitespace (blank or tab) separated columns. Text string columns must be enclosed in quotes if they contain embedded blanks.

For more information about text tables, "page tables$doc/text_tables.doc".

The print format is used by such tasks as tprint, tedit, and tread to determine how the column values are to be displayed. Most of the ordinary Fortran formats are supported for tables. Nonstandard formats should not be used for FITS tables for reasons of portability. The differences between the capabilities of Fortran formats and SPP formats are discussed below.

Here is a list of the default print format for each data type, given in both SPP style and Fortran style.

default formats:

	data type      SPP       Fortran
	---------      ---       -------
	real           %15.7g    G15.7
	double prec    %25.16g   G25.16
	integer        %11d      I11
	short          %11d      I11
	boolean        %6b       L6
	text string    %-ns      A-n

where n for character strings is the string size as given when the column was defined. The minus sign means that the string will be left justified. While a format such as "A-12" is not available in standard Fortran, a format may be given with that syntax when using ttools tasks, and the format will be converted to SPP style.

SPP formats (and Fortran equivalents) that are supported for STSDAS tables are as follows.

	SPP    Fortran      meaning
	---    -------      -------
	 b        L         boolean "yes" or "no"
	 d        I         integer, displayed in decimal
	 x        Z         integer, displayed in hexadecimal
	 e      E or D      exponential format
	 f        F         floating point
	 g        G         use F or E as appropriate
	 h        H         nn:nn:nn.n
	 H      (none)      divide by 15, then nn:nn:nn.n
	 m        M         nn:nn.n
	 M      (none)      divide by 15, then nn:nn.n
	 s        A         character string

The syntax is "%w.dC" (SPP style) or "Cw.d" (Fortran style), where w is the field width, d is the number of decimal places (or precision for g format), and C is the format code as given in the left column below. When giving a format in Fortran style, use the format code given in the second column; these are shown in upper case but may also be given in lower case. Note that H and M are not standard Fortran formats; in particular, H is not interpreted as Hollerith. See below for more information about H and M formats.

The field width (w) may be given as a positive number, a negative number, or preceded by a zero. A negative field width means the value should be left justified in the field. A leading zero means the field should be padded on the left by zeroes; for example, "%04d" or "I04" is equivalent to the standard Fortran "I4.4". The d value means the number of decimal places for f, h, m, H or M format, but it means the digits of precision for g format. For character strings, "%s" means left justify and use only as much space as needed to print the value; "%40s" and "%-40s" mean right and justify respectively in a 40-character field.

When the format is given in SPP style, there are two relatively new formats that are not available in Fortran. Specifying upper case H or M means that the numbers will be divided by 15 before being formatted using h or m format respectively. This is intended for converting hours to degrees. When two table columns contain right ascension and declination, both in decimal degrees, then appropriate formats might be, for example, %12.2H or %9.2M for right ascension and %12.1h for declination. This would print the right ascension in hours, minutes, seconds (or hours and minutes for M format) with two decimals, and would print the declination in degrees, minutes, seconds with one decimal after the seconds.

Here are some examples.

	internal value    format     displayed value
	--------------    ------     ---------------
	2.71828           %10.4g          2.718
	2.71828e27        %10.4g       2.718E27
	2.71828           %10.4f         2.7183
	2.71828           %10.4e        2.718E0
	2.71828           %10.1h      2:43:05.8
	2.71828           %10.1m         2:43.1
	2.71828           %07.1m     02:43.1
	2.71828           %10d                2
	927               %10d              927
	927               %-10d      927
	927               %010d      0000000927
	ttools            %s         ttools
	ttools            %10s           ttools
	ttools            %-10s      ttools

FITS and STSDAS tables can have columns that contain arrays ("3-D tables"). That is, each cell (designated by both a column name and a row number) stores a 1-dimensional array of elements instead of a single value.

There are four tasks that act as 3-D table translators. These tasks extract information from or insert information into "3-D tables".

The information moved from/to a 3-D table by the tasks in this package can have either of two forms, regular 2-D tables or 1-dimensional images. Tasks txtable and titable perform, respectively, extractions and insertions of 2-D tables. Tasks tximage and tiimage perform, respectively, extractions and insertions of images.

Task tscopy is a variant of the tcopy task. It performs a standard table copy but also supports the selector mechanism to allow copying of sections of columns that contain arrays. Type "help selectors" for further information about sections.

SEE ALSO

selectors
files in tables$doc/


Source Code · Search Form · STSDAS