3.7 Layout and Data Transformations

SDDS++ provides transformation operations without requiring an application to reimplement the SDDS type system:

• LayoutEditor copies, renames, replaces, drops, or adds parameter, array, column, and associate definitions.
• RowView reads an individual row without copying column data.
• RowMask supports intersection, union, inversion, and typed row matching. Page::filtered applies a mask to a page.
• convertScalar and convertValues perform checked conversions with an explicit rounding policy where necessary.
• convertUnits changes a field’s units and multiplies its data in one operation, keeping metadata and values consistent.
• Page::matrix<T> creates a contiguous row-major DenseMatrix<T> from selected numeric columns using exact types or checked conversion.
• copyDataset streams pages through optional layout and page transformations without materializing the complete input file.

Transformation output is governed by the originating reader’s resource limits. Layout transformations supplied to copyDataset should agree with the page transformations; the destination writer validates each resulting page against the transformed layout.