S-Lang function to read a file in RDB format.
Struct_Type readrdb( filename )
Struct_Type readrdb( filename, axes )
Struct_Type readrdb( filename, axes, nskip )
Error Return Value: NULL
Arguments:
filename is a String_Type variable
cols is either a String_Type variable or an Int_Type array
nskip is an Int_Type variable
The readrdb() function allows you to read in data from
RDB files into S-Lang.
The ahelp page for readfile describes the features of this
routine that are common to all the "read" functions provided
by the Varmm module. This page describes those features that
are unique to the readrdb() command.
The filename argument should be a string that contains the
name of the file to be read in. Unlike the other "read"
functions it can not include any Data-Model syntax.
The optional parameter "cols" is a list of column names, or numbers,
to be read, and "nskip" is the number of rows to be skipped.
As examples:
chips> r1 = readrdb( "table.rdb" )
chips> r2 = readrdb( "table.rdb","1,3,5", 10 )
where the second example only reads in the first, third, and
fifth columns and skips the first ten lines of the files.
RDB files are ASCII files which use tabs to separate
columns. They can contain a mixture of numeric and character
columns, along with metadata and header information.
Information on RDB, along with tools to access these files,
is available from
ftp://ftp.rand.org/pub/RDB-hobbs/.
The header of an RDB file is optional and is marked by
a set of lines beginning with the "#" character.
The first non-comment line gives the names of the fields
as a set of names sepearated by tabs.
The following line gives the type and sugested
length of each column; again each volumn is separated by a tab
character.
Finally comes the actual data in tab-separated columns.
The function returns a structure whose fields contain the
data read in from the file. If an error occurred - such
as the file not being found, or it is not a RDB file -
then NULL is returned instead.
The returned structure follows the format of the other
"read" functions: metadata - i.e. information about the
file - is stored in fields beginning with an underscore
character followed by fields containing the input data.
The initial fields are discussed in "ahelp readfile";
here we concentrate on those fields specific to
RDB files.
Fields specific to tables:
| _header |
This is a String_Type array that lists the header
information of the RDB file. It does not use
FITS format.
|
| _ncols |
The number of columns read from the file.
|
| _nrows |
The number of rows read from the file.
|
| <column 1> |
Contains the data for the first column
read in. The name of the column matches
the name from the rdb file.
|
| <column 2> |
Contains the data for the second column
read in.
|
If table.rdb contains:
# Table documentation lines. These describe and
# identify the rdbtable contents.
# They may be read by many normal UNIX utilities,
# which is useful to easily identify a file.
# May also contain RCS or SCCS control information.
NAME COUNT TYP AMT OTHER RIGHT
6 5N 3 5N 8 8>
Bush 44 A 133 Another This
Hansen 44 A 23 One Is
Jones 77 X 77 Here On
Perry 77 B 244 And The
Hart 77 D 1111 So Right
Holmes 65 D 1111 On Edge
where the columns are separated by
the tab character, rather than by spaces,
then we can read it in using:
chips> rdb = readrdb( "table.rdb" )
chips> print( rdb )
_filename = table.rdb
_path = /data/analysis/
_filter = NULL
_filetype = 2
_header = String_Type[5]
_ncols = 6
_nrows = 5
NAME = String_Type[5]
COUNT = Double_Type[5]
TYP = String_Type[5]
AMT = Double_Type[5]
OTHER = String_Type[5]
RIGHT = String_Type[5]
and some of the fields contain:
chips> print( rdb._header )
# Table documentation lines. These describe and
# identify the rdbtable contents.
# They may be read by many normal UNIX utilities,
# which is useful to easily identify a file.
# May also contain RCS or SCCS control information.
chips> writeascii( stdout, rdb.NAME, rdb.AMT )
Bush 133
Hansen 23
Jones 77
Perry 244
Hart 1111
There are now separate ahelp files for the individual
functions, rather than having all the information
placed into this document.
A new field called "_filetype" has been added to the data structure
which describes the type of the file read in.
The contents of the field are described in the
"Format of data structure" section above.
The readrdb() routine has been added to allow reading in of
RDB files. Note that readfile() does not recognise RDB files, so
you have to call readrdb() directly.
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