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6.2 Specifying a Single Column

If an argument is specified in the help text for a command with the symbol <col-id> it means you must give a string which identifies one of the existing columns in a table.

There are three ways you can specify a column in this context:

Column Name
The name of the column may be used if it contains no spaces and doesn't start with a minus character ('-'). It is usually matched case insensitively. If multiple columns have the same name, the first one that matches is selected.
Column Index or $ID
The index of the column may always be used; this is a useful fallback if the column name isn't suitable for some reason. The first column is '1', the second is '2' and so on. You may alternatively use the forms '$1', '$2' etc.

Tip: if counting which column has which index is giving you a headache, running tpipe with omode=meta or omode=stats on the table may help.

Column ucd$ specifier
If the column has a Unified Content Descriptor (this will usually only be the case for VOTable or possibly FITS format tables) you can refer to it using an identifier of the form "ucd$<ucd-spec>". Depending on the version of UCD scheme used, UCDs can contain various punctuation marks such as underscores, semicolons and dots; for the purpose of this syntax these should all be represented as underscores ("_"). So to identify a column which has the UCD "phot.mag;em.opt.R", you should use the identifier "ucd$phot_mag_em_opt_r". Matching is not case-sensitive. Futhermore, a trailing underscore acts as a wildcard, so that the above column could also be referenced using the identifier "ucd$phot_mag_". If multiple columns have UCDs which match the given identifer, the first one will be used.
Column utype$ specifier
If the column has a Utype (this will usually only be the case for VOTable or possibly FITS format tables) you can refer to it using an identifier of the form "utype$<utype-spec>". Utypes may contain various punctuation marks such as colons and dots; for the purpose of this syntax these should all be represented as underscores ("_"). So to identify a column which has the Utype "ssa:Access.Format", you should use the identifier "utype$ssa_Access_format". Matching is not case-sensitive. If multiple columns have Utypes which match the given identifier, the first one will be used.


Next Previous Up Contents
Next: Specifying a List of Columns
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Previous: uniq

STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk