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#### 6.1.12 `constcol`

Usage:

       constcol [-noparam] [-acceptnull] [-[no]parallel] [<colid-list>]

Identifies columns with constant values. Such columns are removed from the table and by default their fixed value is added to the table as a table parameter with the same name as the removed column. Such columns may have scalar or array values.

The `-noparam` flag controls whether constant columns identified are recorded instead as table parameters (per-table metadata items). By default they are, but supplying `-noparam` means these values will just be discarded.

The `-acceptnull` flag controls how blank values in candidate columns are treated. By default, all values in a column must be strictly the same for a column to be identified as constant value, but if `-acceptnull` is supplied then a column will be treated as constant if all its entries are either a single fixed value or blank.

The `-[no]parallel` flag controls whether processing is done using multithreading for large tables.

The `<colid-list>` gives the columns to be assessed by this filter; if not supplied, all columns will be examined.

Syntax for the `<colid-list>` argument is described in Section 6.3.

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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