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Patch Transform
Use patch to update or add columns while keeping everything else. Like map, but unspecified columns are preserved.
Replace a Column
$ Replace a Column
Columns named in the patch are replaced. Everything else stays unchanged.
Add New Columns
$ Add New Columns
Columns that don't exist yet are appended at the end.
Expressions
$ Expressions
Patch assignments can use expressions referencing existing columns.
Chaining Patches
$ Chaining Patches
Chain patches when later columns depend on earlier ones.
Patch updates the row shape — matched columns are replaced, new columns are added, and unmatched columns survive. Map replaces the row shape entirely. Extend adds columns but cannot replace existing ones. Use patch when you want to selectively update without losing anything.