polaris.attrs.set_attrs

polaris.attrs.set_attrs(da: DataArray, long_name: str | None = None, units: str | None = None, **extra: str) → DataArray[source]

Replace the attributes of da in place with the given metadata.

Any attributes da already has are discarded, not merged. This is the point of the helper: xarray propagates attrs through arithmetic, comparisons, where() and zeros_like(), so a variable computed from another arrives carrying its parent’s metadata. Setting individual keys (da.attrs['units'] = ...) leaves the rest of the parent’s metadata behind, which is how level indices and masks derived from a seafloor pressure ended up labelled as pressures in Pascals.

The array is modified in place and also returned, so either call pattern works:

ds['minLevelCell'] = min_level_cell + 1
set_attrs(ds.minLevelCell, long_name='Index to the first ...')

ds['bottomDepth'] = set_attrs(
    -geom_z_bot, long_name='seafloor geometric depth', units='m'
)

Parameters:

da (xarray.DataArray) – The variable to label. Its existing attributes are discarded.
long_name (str, optional) – The long_name attribute. Omitted from the result if None.
units (str, optional) – The units attribute. Omitted from the result if None. Leave it out for quantities with no meaningful unit, such as one-based level indices, rather than inventing one.
extra (str) – Any further attributes to set, such as note or standard_name.

Returns:

xarray.DataArray – da, so the call can be used inline in an assignment.