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### 7.2 Referencing Row Subset Flags

If you have any Row Subsets defined you can also access the value of the boolean (true/false) flag indicating whether the current row is in each subset. Again there are two ways of doing this:

By Name
  The name assigned to the subset when it was created can be used if it is unique and if it has a suitable form. The same comments apply as to column names above.
By _ID
  The "_ID" identifier of the subset may always be used to refer to it. Like the "$ID" identifier for columns above, this is a unique integer preceded by a special symbol, this time the underscore, "_".

  Note: in early versions of TOPCAT the hash sign ("#") was used instead of the underscore for this purpose; the hash sign no longer has this meaning.

In either case, the value will be a boolean value; these can be useful in conjunction with the conditional "`? :`" operator or when combining existing subsets using logical operators to create a new subset.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk