Selecting DataArrays¶

See also

CF conventions on

A powerful feature of cf_xarray is the ability select DataArrays using special “CF names” like the “latitude”, or “longitude” coordinate names, “X” or “Y” axes names, oreven using the standard_name attribute if present.

To demonstrate this, let’s load a few datasets

from cf_xarray.datasets import airds, anc, multiple, popds as pop

By axis and coordinate name¶

Lets select the "X" axis on airds.

# identical to airds["lon"]
airds.cf["X"]

<xarray.DataArray 'lon' (lon: 50)> Size: 200B
200.0 202.5 205.0 207.5 210.0 212.5 ... 310.0 312.5 315.0 317.5 320.0 322.5
Coordinates:
  * lon      (lon) float32 200B 200.0 202.5 205.0 207.5 ... 317.5 320.0 322.5
Attributes:
    standard_name:  longitude
    long_name:      Longitude
    units:          degrees_east
    axis:           X

This works because airds.lon.attrs contains axis: "X"

airds.cf

Coordinates:
             CF Axes: * X: ['lon']
                      * Y: ['lat']
                      * T: ['time']
                        Z: n/a

      CF Coordinates: * longitude: ['lon']
                      * latitude: ['lat']
                      * time: ['time']
                        vertical: n/a

       Cell Measures:   area: ['cell_area']
                        volume: n/a

      Standard Names: * latitude: ['lat']
                      * longitude: ['lon']
                      * time: ['time']

              Bounds:   n/a

       Grid Mappings:   n/a

Data Variables:
       Cell Measures:   area, volume: n/a

      Standard Names:   air_temperature: ['air']

              Bounds:   n/a

       Grid Mappings:   n/a

By `cf_role`¶

cf_xarray supports identifying variables by the cf_role attribute.

ds = xr.Dataset(
    {"temp": ("x", np.arange(10))},
    coords={"cast": ("x", np.arange(10), {"cf_role": "profile_id"})}
)
ds.cf["profile_id"]

<xarray.DataArray 'cast' (x: 10)> Size: 80B
0 1 2 3 4 5 6 7 8 9
Dimensions without coordinates: x
Attributes:
    cf_role:  profile_id