Next: FITS files, Previous: Array input output, Up: Gnuastro library [Contents][Index]
Tables are a collection of one dimensional datasets that are packed together into one file. They are the single most common format to store high-level (processed) information, hence they play a very important role in Gnuastro. For a more thorough introduction, please see Table. Gnuastro’s Table program, and all the other programs that can read from and write into tables, use the functions of this section for reading and writing their input/output tables. For a simple demonstration of using the constructs introduced here, see Library demo - reading and writing table columns.
Currently only plain text (see Gnuastro text table format) and FITS (ASCII and binary) tables are supported by Gnuastro. However, the low-level table infra-structure is written such that accommodating other formats is also possible and in future releases more formats will hopefully be supported. Please don’t hesitate to suggest your favorite format so it can be implemented when possible.
The default width and precision for generic types to use in writing numeric
types into a text file (plain text and FITS ASCII tables). When the dataset
doesn’t have any pre-set width and precision (see disp_width and
disp_precision in Generic data container (gal_data_t)) these will be
directly used in C’s printf command to write the number as a string.
The display format used in C’s printf to display data of different
types. The _STRING and _DECIMAL are unique for printing
strings and signed integers, they are mainly here for
completeness. However, unsigned integers and floating points can be
displayed in multiple formats:
For unsigned integers, it is possible to choose from _UDECIMAL
(unsigned decimal), _OCTAL (octal notation, for example 125
in decimal will be displayed as 175), and _HEX (hexadecimal
notation, for example 125 in decimal will be displayed as
7D).
For floating point, it is possible to display the number in _FLOAT
(floating point, for example 1500.345), _EXP (exponential,
for example 1.500345e+03), or _GENERAL which is the best of
the two for the given number.
All the current acceptable table formats to Gnuastro. The AFITS and
BFITS represent FITS ASCII tables and FITS Binary tables. You can
use these anywhere you see the tableformat variable.
When the desired column is not a number, these values determine if the
string to match, or regular expression to search, be in the name,
units or comments of the column meta data. These values
should be used for the searchin variables of the functions.
*filename, char *hdu, gal_list_str_t *lines, size_t *numcols, size_t *numrows, int *tableformat)Store the information of each column of a table into an array of data
structures with numcols datasets (one data structure for each
column). The number of rows is stored in numrows. The format of the
table (e.g., ASCII text file, or FITS binary or ASCII table) will be put in
tableformat (macros defined above). If the filename is not a
FITS file, then hdu will not be used (can be NULL).
The input must be either a file (specified by filename) or a list of
strings (lines). lines is a list of strings with each node
representing one line (including the new-line character), see List of strings. It will mostly be the output of gal_txt_stdin_read, which
is used to read the program’s input as separate lines from the standard
input (see Text files (txt.h)). Note that filename and lines
are mutually exclusive and one of them must be NULL.
In the output datasets, only the meta-data strings (column name, units and comments), will be allocated and set. This function is just for column information (meta-data), not column contents.
*allcols, size_t numcols, size_t numrows)This program will print the column information for all the columns (output
of gal_table_info). The output is in the same format as this command
with Gnuastro Table program (see Table):
$ asttable --info table.fits
*filename, char *hdu, gal_list_str_t *lines, gal_list_str_t *cols, int searchin, int ignorecase, size_t minmapsize, int quietmmap, size_t *colmatch)Read the specified columns in a file (named filename), or list of
strings (lines) into a linked list of data structures. If the file
is FITS, then hdu will also be used, otherwise, hdu is
ignored.
lines is a list of strings with each node representing one line
(including the new-line character), see List of strings. It will
mostly be the output of gal_txt_stdin_read, which is used to read
the program’s input as separate lines from the standard input (see
Text files (txt.h)). Note that filename and lines are mutually
exclusive and one of them must be NULL.
The information to search for columns should be specified by the
cols list of strings (see List of strings). The string in each
node of the list may be a number, an exact match to a column name, or a
regular expression (in GNU AWK format) enclosed in / /. The
searchin value must be one of the macros defined above. If
cols is NULL, then this function will read the full table.
The output is an individually allocated list of datasets (see List of gal_data_t) with the same order of the cols list. Note that one
column node in the cols list might give multiple columns (for
example from regular expressions), in this case, the order of output
columns that correspond to that one input, are in order of the table (which
column was read first). So the first requested column is the first popped
data structure and so on.
if colmatch!=NULL, it is assumed to be an array that has at least the
same number of elements as nodes in the cols list. The number of
columns that matched each input column will be stored in each element.
*cols, gal_data_t *allcols, size_t numcols, int searchin, int ignorecase, char *filename, char *hdu, size_t *colmatch)Returns a list of indexs (starting from 0) of the input columns that match
the names/numbers given to cols. This is a low-level operation which
is called by gal_table_read (described above), see there for more on
each argument’s description. allcols is the returned array of
gal_table_info.
**comments, char *program_string, time_t *rawtime)Add some basic information to the list of comments. This basic
information includes the following information
COMMIT in Output FITS files).
rawtime (time_t is C’s
calendar time format defined in time.h). You can calculate the time
in this format with the following expressions:
time_t rawtime; time(&rawtime);
program_string. If it is NULL,
this line is ignored.
*cols, struct gal_fits_list_key_t **keywords, gal_list_str_t *comments, int tableformat, char *filename, char *extname, uint8_t colinfoinstdout)Write cols (a list of datasets, see List of gal_data_t) into a
table stored in filename. The format of the table can be determined
with tableformat that accepts the macros defined above. When
filename==NULL, the column information will be printed on the
standard output (command-line).
If comments!=NULL, the list of comments (see List of strings)
will also be printed into the output table. When the output table is a
plain text file, every node of comments will be printed after a
# (so it can be considered as a comment) and in FITS table they will
follow a COMMENT keyword.
If a file named filename already exists, the operation depends on
the type of output. When filename is a FITS file, the table will be
added as a new extension after all existing extensions. If filename
is a plain text file, this function will abort with an error.
If filename is a FITS file, the table extension will have the name
extname.
When colinfoinstdout!=0 and filename==NULL (columns are
printed in the standard output), the dataset metadata will also printed in
the standard output. When printing to the standard output, the column
information can be piped into another program for further processing and
thus the meta-data (lines starting with a #) must be ignored. In
such cases, you only print the column values by passing 0 to
colinfoinstdout.
*logll, char *program_string, time_t *rawtime, gal_list_str_t *comments, char *filename, int quiet)Write the logll list of datasets into a table in filename
(see List of gal_data_t). This function is just a wrapper around
gal_table_comments_add_intro and gal_table_write (see
above). If quiet is non-zero, this function will print a message
saying that the filename has been created.
Next: FITS files, Previous: Array input output, Up: Gnuastro library [Contents][Index]
GNU Astronomy Utilities 0.14 manual, January 2021.