xarray

xarray best practices

units / quantities

baseline

• as of now, using pint.Quantity as data for xr.DataArray seems to be supported for most use-cases.
• pint.Quantity is not supported in xarray coordinates. Units will get stripped (with the usual pint warning) !

best practices

• in general, all xarray objects should always have a unit-information !
  For dimensionless units use the pint-default of "".
• use pint.Quantity for data whenever possible
• for time-like" coordinates use numpy/pandas time-types/Index-types like pd.DatetimeIndex,pd.Timedeltaindex,datetime64[ns] etc.
• In cases where pint.Quantity cannot be used (i.e. coordinates) store the unit in .attrs["units"]
  (follow the guidelines as per https://github.com/xarray-contrib/pint-xarray to ensure maximum compatibility for future updates.)

validating xarray coordinate structures

To validate the coordinate layout of a specific xarray object us weldx.utility.xr_check_coords. Currently checking for dtype and specific values is supported. Unit support should be added later.

weldx xarray Accessors

Custom xarray Accessors should be registered under "weldx" (see weldx.utility). Currently accessors are not actively used.

naming conventions (up for discussion)

A small list of naming conventions to use throughout weldx with regards to internal xarray dimensions/coordinates.

• time-axis coordinates should be name "time"
  • dtype for time-axis should either be datetime64 or timedelta64
  • when associating values stored as timedelta64 with a reference time the reference time should be stored in .attrs["time_ref"]
• Cartesian-Coordinates should be named "c" and consist of values ["x","y","z"]
• a (dimensionless) variable describing progression along a trace should run from 0 to 1 and be named "s"