<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 98.1p1 release (March 2nd, 1998) originally by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>General advice about table files</TITLE> <META NAME="description" CONTENT="General advice about table files"> <META NAME="keywords" CONTENT="vol2"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <LINK REL="STYLESHEET" HREF="vol2.css"> <LINK REL="previous" HREF="node262.html"> <LINK REL="up" HREF="node253.html"> <LINK REL="next" HREF="node264.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html4717" HREF="node264.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html4714" HREF="node253.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html4710" HREF="node262.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html4716" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html4718" HREF="node264.html">Planning your observing run</A> <B> Up:</B> <A NAME="tex2html4715" HREF="node253.html">Getting started</A> <B> Previous:</B> <A NAME="tex2html4711" HREF="node262.html">Instrument file</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION001825000000000000000"> General advice about table files</A> </H2> <P> The MIDAS table file system contains several commands for editing and modifying table files. Columns can be re-named, added, or deleted; various operations can be performed on column contents, and the results stored in a new column; and so on. You should read the on-line help for all the commands with the TABLE qualifier, just to see what operations are supported. <P> One common problem arises with columns that contain character strings. When you create a table from an ASCII file, the width of the table column is (by default) the width of the field in the original *.dat file. Later, you may want to add information to such a column, but find that the existing table column is too narrow to hold the whole string. For example, you might want to add aliases to the OBJECT names, or expand a COMMENT column. <P> The column cannot be made wider by the <TT>EDIT/TABLE</TT> command; however, there is a way to widen it. First, use the ``concat'' operation of <TT>COMPUTE/TABLE</TT> to add a string of blanks to the existing column, and store the widened column under a temporary name. Then delete the original column, and rename the new column with the old name. <P> You can avoid this problem by specifying a width wider than the original ASCII field by using (say) C*32 instead of just C for the column in the format file, when you create the table. Specifying the width in the format file overrides the default width. However, you may find that this wastes a lot of disk space if the column is mostly blanks. <P> <HR> <!--Navigation Panel--> <A NAME="tex2html4717" HREF="node264.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html4714" HREF="node253.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html4710" HREF="node262.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html4716" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html4718" HREF="node264.html">Planning your observing run</A> <B> Up:</B> <A NAME="tex2html4715" HREF="node253.html">Getting started</A> <B> Previous:</B> <A NAME="tex2html4711" HREF="node262.html">Instrument file</A> <!--End of Navigation Panel--> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
