Data array management (rename / drop / keep)

data_rename, data_drop and data_keep rewrite which data arrays a mesh carries and under what names. Values, dtypes and shapes are copied verbatim, and the geometry comes through bit-identical. They are data operations, not file formats.

import meshioplusplus as mp

mesh = mp.read("part.vtu")

mesh = mp.data_rename(mesh, "point", "T", "temperature")   # rename one array
mesh = mp.data_drop(mesh, "point", ["scratch", "tmp"])     # remove by name
mesh = mp.data_keep(mesh, "cell", ["material"])            # keep only these

For several changes at once, data_manage applies them in one pass and reports what it did:

result = mp.data_manage(
    mesh,
    keep=[("point", "T"), ("point", "p")],
    drop=[("cell", "scratch")],
    rename=[("point", "T", "temperature")],
)
result["mesh"]      # the rewritten mesh
result["dropped"]   # ["cell_data:scratch", "point_data:u", ...] (sorted)
result["renamed"]   # [("point_data:T", "point_data:temperature")]

Phase order

The three phases apply in a fixed, documented order: keep, then drop, then rename.

keep is a whitelist that only affects the locations it actually mentions — so keeping some point_data arrays leaves cell_data and field_data completely untouched. data_keep(mesh, "point", []) is meaningful: it drops every point_data array while leaving the other locations alone.

Errors

An unknown key raises ValueError listing every key that is present:

meshio++: no point_data array named 'foo' (available: T, p, u)

Pass ignore_missing=True to skip absent keys instead. A rename whose target already exists also raises, unless that target is itself renamed away or dropped in the same pass — which makes swapping two names legal:

# Legal: neither target survives under its old name.
mp.data_manage(mesh, rename=[("point", "a", "b"), ("point", "b", "a")])

Two renames targeting the same name, or two renames of the same source, always raise.

CLI

meshioplusplus data rename in.vtu out.vtu --point T:temperature
meshioplusplus data drop   in.vtu out.vtu --point a,b --cell c
meshioplusplus data keep   in.vtu out.vtu --point T,p --cell mat

--point, --cell and --field select the location. For rename the OLD:NEW value is split on the last colon, because data names routinely contain colons — so --point gmsh:physical:tag renames gmsh:physical to tag. --point is repeatable for rename; for drop/keep it takes a comma-separated list. See the CLI reference.

Other languages

• C API — mio_data_drop, mio_data_keep and mio_data_rename each return a new mio_mesh*. Name lists cross as const char* const* names plus an explicit int64_t count. The combined data_manage is deliberately not exposed; the three primitives compose. See the C API reference.
• Fortran — m%data_drop(MIO_DATA_POINT, ["T"]), m%data_keep(...), m%data_rename(MIO_DATA_POINT, "T", "temperature"). See the Fortran reference.
• WebAssembly / JavaScript — dataDrop(mesh, "point", ["T"], false), dataKeep(...), dataRename(mesh, "point", "T", "temperature"). See the WebAssembly reference.