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#### 6.1.10 `collapsecols`

Usage:

       collapsecols [-[no]keepscalars] <array-colname> <col-id0> <ncol>

Adds a new array-valued column by using the values from a specified range of scalar columns as array elements. The new column is named `<array-colname>`, and produced from the sequence of `<ncol>` scalar columns starting with `<col-id0>`.

The array type of the output column is determined by the type of the first input column (`<col-id0>`). If it is of type `Double`, the output array column will be a `double[]` array, and similarly for types `Long`, `Integer`, `Float` and `Boolean`. Other integer types are currently mapped to `int[]`, and object types, e.g. `String`, to the corresponding array type. Array elements for null or mistyped input values are mapped to NaN for floating point types, but note that they currently just turn into zeros for integer array types and `false` for boolean.

By default the scalar columns that have been used are removed from the output table and the new column replaces them at the same position. However, if you supply the `-keepscalars` flag they will be retained alongside the new array column (the new column will appear just after the run of scalar columns).

This filter does the opposite of `explodecols`.

Syntax for the `<col-id0>` argument is described in Section 6.2.

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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